Wound dressing with micropump

ABSTRACT

A composite wound dressing apparatus promotes healing of a wound via the use of a micropump system. The micropump system includes a micropump that applies a subatmospheric pressure to the wound to effectively draw wound fluid or exudate away from the wound bed, or deliver fluids to the wound bed, without the need for a cumbersome external pressure (e.g. vacuum) source. Hence, the wound dressing and micropump system is portable which allows the patient mobility that is unavailable when an external vacuum source is used.

FIELD OF THE INVENTION

The present disclosure relates to an apparatus for treating an openwound, and, more specifically, relates to a wound dressing with amicropump adapted for both introducing fluids into and evacuating fluidsfrom a wound to facilitate the wound healing process.

BACKGROUND

Wound closure involves the migration of epithelial and subcutaneoustissue adjacent the wound towards the center of the wound until thewound closes. Unfortunately, closure is difficult with large wounds orwounds that have become infected. In such wounds, a zone of stasis (i.e.an area in which localized swelling of tissue restricts the flow ofblood to the tissues) forms near the surface of the wound. Withoutsufficient blood flow, the epithelial and subcutaneous tissuessurrounding the wound not only receive diminished oxygen and nutrients,but, are also less able to successfully fight microbial infection and,thus, are less able to close naturally. Such wounds have presenteddifficulties to medical personnel for many years.

For example, skin ulcers are a common problem among many diabetics, andare often brought on by poor blood circulation and nerve damageassociated with diabetes and/or vascular disease. The treatment of suchulcers often involves grafting skin from a relatively healthy donor siteto an ulcerous wound site. Split thickness surgical skin grafttechniques may be employed to obtain skin grafts from donor sites thatcan then heal spontaneously. Full thickness skin grafts, on the otherhand, generally require closure of the donor site. Furthermore, manywounds can become stalled in a “chronic condition” in which furtherhealing does not occur and, in fact, wound may actually increase in sizeand depth.

Wound dressings have been used in the medical industry to protect and/orfacilitate healing of open wounds. Although various types of dressingmaterials have been successfully employed, membranes comprisingsemi-permeable materials are often preferred because they can increasepatient comfort and lower the risk of infection. Semi-permeablemembranes generally pass moisture vapors, but are generally imperviousto liquids. Thus, they can promote healing by permitting a wound site to“breathe”. An industry standard is Tegaderm™ sold by 3M Company, St.Paul, Minn. Although transparent dressings can “breathe”, they often donot have sufficient moisture vapor transmission rates (MVTR) to allowevaporation of excess wound fluid exudate. If allowed to accumulateand/or remain over the wound optimal wound healing will not occur.

In surgical wounds this is alleviated by using a wound drain thatremoves excess fluid to a remote container using an applied vacuum(reduced pressure). Use of wound drains often uses a separate incisionto introduce the drain. Many wound dressings for chronic wounds absorbexcess wound fluid. Examples include hydrocolloid adhesive dressings,absorbent foam dressings, alginate dressings, hydrogel dressings and thelike. While these dressings absorb excess wound fluid they can becomesaturated and allow wound fluid to build up in highly exuding wounds.Further they will not optimize the wound healing environment for woundsthat tend to remain dry. These dry wounds may be characterized byinsufficient blood flow to the wound bed.

Another technique has been to use negative pressure therapy, which isalso known as suction or vacuum therapy. These devices apply a vacuum toa wound bed beneath a film dressing. In addition to removing excesswound fluid, the vacuum is believed to allow flow of interstitial fluidinto the wound bed to promote healing. Commercial devices are sold byKCI under the “Wound Vac” tradename and by Smith and Nephew (formerlyBluesky Medical) under the tradename “VISTA”. These devices comprise amotorized electric vacuum pump, wound dressing and a wound fluid trap.The wound pumps are reusable so to minimize contamination of otherpatients a fluid trap is placed between the vacuum pump and the wounddressing. Thus, when the trap is filled the therapy must be interruptedto change the trap. Finally, since the entire system operates at reducedpressure it becomes difficult, if not impossible, to remove a woundfluid sample for analysis without interrupting therapy. These systemsare generally large and may not be easily portable.

Smaller systems have been suggested such as in US Patent ApplicationPublication No. 2007/0078366 A1 which discloses a composite wounddressing apparatus consisting of a multilayer wound dressing and amicropump. The wound dressing is described as having a base layer, apacking layer, an absorbent layer, and a top sheet. The top sheet issaid to be sealed to seal the wound dressing (paragraph 0032). Paragraph0034 states that “The micropump 120 may be embedded within the absorbentlayer 106 or mounted to the layer 106, or alternatively associatedwithin the confines of the wound dressing 100.” Thus, during operationthe micropump is sealed within the cavity formed by the wound dressingand the wound, as illustrated in FIGS. 1, 2, 4 and 6 of US PatentApplication Publication No. 2007/0078366. The micropump is said to pulla vacuum on the wound bed (see e.g. paragraph 0034). This appearsfundamentally impossible with the arrangement disclosed. Because themicropump is located within a sealed cavity having no exit from thedressing, a vacuum cannot be generated without exhausting fluid (air orliquid) from the wound cavity. As described and illustrated the inletand outlet of the micropump are both within the wound cavitycompartment.

A further problem with the composite dressing design disclosed in USPatent Publication No. 2007/0078366 is that many (or perhaps most)wounds that require vacuum therapy can generate large volumes of fluid.The disclosure provides that removal of fluid from the dressing occursby opening an access door (see paragraph 0033) and removing thesaturated absorbent layer. For many wounds this could require frequentchanges which is inconvenient, unnecessarily exposes the healthcareworker to body fluids, and requires significantly more labor thancurrent systems which collect the exudate into a canister.

Ease of use, efficiency of healing a wound, and a source of constantnegative pressure are ongoing issues that need to be addressed bycontinuing improvements in wound therapy.

SUMMARY OF THE INVENTION

The wound dressing micropump system of the present invention comprises awound dressing, micropump, and fluid accumulation device. The wounddressing comprises an adhesive coated optionally, a thin film dressingoptionally with a valve or other micropump attachment means. Themicropump is placed between the dressing and the fluid accumulationdevice such that the fluid enters the inlet side of the micropump fromthe wound dressing and exits to the fluid accumulation device underpositive pressure. In a preferred embodiment the micropump is integralwith the dressing and driven by a small battery power source. The fluidaccumulation device may be as simple as a bag or canister, canoptionally incorporate fluid absorbents such as supersorbents, and mayoptionally comprise a vent.

In one preferred embodiment, a wound dressing apparatus includes a wounddressing dimensioned for positioning relative to a wound bed and amicropump system. The micropump system includes a micropump for applyingsubatmospheric pressure to at least the wound dressing to facilitateremoval of fluid from the wound bed and promote the flow of interstitialfluid into the wound bed. The micropump is preferably mounted on thewound dressing such that it is integral with the wound dressing. Inanother preferred embodiment the micropump is in fluid communicationwith the wound dressing. The preferred micropump is adapted to producesubatmospheric pressure ranging from about 5 mmHg to about 500 mmHg andpreferably ranging from about 25 mmHg to about 250 mmHg belowatmospheric pressure.

Preferred micropumps operate without an electric motor (i.e. do not havea rotor). The preferred micropumps utilize elastomeric diaphragms tomove air and wound fluid. As used herein a “micropump” means a micropumpwith an actuator dimension of less than about 20 cm², preferably lessthan 10 cm², and most preferably less than about 8 cm². In the case ofmicropumps with multiple actuators the actuator dimension area iscalculated in total.

In a preferred embodiment, the micropump is low cost and disposablewhich can reduce infection transmission. Furthermore, the preferredmicropump dressing system can remove fluid from the wound using areduced pressure (less than atmospheric pressure, i.e. a vacuum) but canalso micropump the fluid to an accumulation device under positivepressure (greater than atmospheric pressure).

The present invention discloses a wound micropump made by using anelecroactive (such as a Piezoelectric or electrostrictive) diaphragm.The diaphragm is preferably constructed at least in part from anelectroactive film that provides mechanical deformation in response toapplied electric field, and thus serves as an actuator.

Unlike other types of wound vacuum systems, the configuration of thesystem disclosed eliminates the use of “fluid traps” which can becomefilled and thus contaminate the reusable motorized micropumps associatedtherewith. Such systems also must be shut down in order to drain thetrap. The positive pressure wound fluid accumulation devices of thepresent invention may be replaced without interrupting the woundtherapy. Finally, the micropump dressing systems are significantlysmaller than prior art negative pressure therapy devices, lesscomplicated, and quiet. This allows for greater patient comfort and easyambulation for those patients that are capable.

The preferred wound dressing includes a backing layer with an interiorportion surrounded by a perimeter. The backing includes a skin contactsurface with an adhesive coating. The adhesive coating may be applied toall or a portion of the wound dressing but is at least applied to theskin contact perimeter. The adhesive may or may not be applied over theinterior wound contact portion. The backing layer is further describedbelow, and preferably comprises a breathable semi-permeable materialfilm that is able to pass moisture vapors but is generallyimperviousness to liquids to prevent bacterial contamination and toensure an adequate vacuum can be applied to the treatment area. Theadhesive coating should likewise be semi-permeable and may be acontinuous or discontinuous pattern. Discontinuous patterns may beprinted or coated engineered designs or may be random patterns.Discontinuous random patterns may be created for example, by using ablown microfiber (BMF) pressure sensitive adhesive. Although thepreferred embodiments use an adhesive to form a seal, dressings are alsocontemplated that do not have an adhesive coating and seal over thewound, such as a circumferential wrap around a limb or abdomen.

The wound dressing may optionally include at least one of a number ofactives including for example, medicaments, anti-infective agents,antimicrobials, antiseptics (for example polyhexamethylene biguanide(hereinafter, “PHMB”), chlorhexidine, silver, iodine, an iodophor,benzalkonium chloride, hydrogen peroxide as well as the antisepticsdisclosed in the following pending applications: US 2005/0089539,US2006/0051385, US2006/0052452, and US2006/0051384 which areincorporated herein by reference), antibiotics, analgesics, localanesthetics, anti-inflammatory agents, healing factors, vitamins, growthfactors, enzyme inhibitors such as matrix metalloproteinase (MMP)inhibitors, and nutrients and/or one of a microbead packing and/orabsorbent foam. Such actives may be introduced by elution off of anyportion of the wound dressing including the backing, adhesive or porousfilter, or from a separate storage chamber that allows controlledintroduction of the medication into the wound space due to the reducedpressure environment. Alternatively, medication may be introduced astaught in U.S. Pat. No. 6,867,342 or by injecting the medicationdirectly through the dressing.

A wound dressing may also comprise a porous filter component whichserves to filter out large debris that may clog the micropump. In oneembodiment the porous filter comprises an intermediate layer of woundpacking material placed between a wound site and the cover dressing. Theintermediate layer can comprise a variety of wound packing materialswith varying properties such as absorbency, wicking or capillary action,and surface contact action. The intermediate material layer is primarilylocated in a chamber formed between the wound (treatment area) and thedressing.

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere in thespecification.

The term “electrically responsive” refers to an element which may store,develop or accept an electrical charge. These elements typicallycomprise alternating layers of conductive and nonconductive materials.

The term “cutting plane” (i.e., cutting location) refers to an imaginaryplane in relation to a three-dimensional object. For example, a cuttingplane oriented in a y-z plane is useful for separating individualelectrically responsive elements. The cutting plane or cutting locationis perpendicular to the x-dimension of the article for dividing theelements, where faces of the alternating conductive regions of theconductive layer are exposed and coincident to one of the two faces ofthe element after separation.

The term “unit cell” refers to the element which repeats or extendsalong a dimension being divisible. For example, a unit cell for anelectrically responsive element comprises at least one nonconductivelayer and at least two conductive layers. The nonconductive layer islocated in between the conductive layers. The unit cell is separablefrom a plurality of unit cells extending in the x-dimension at a y-zcutting plane.

The term “interstices” refers to a space between things or parts. Forexample, the interstices between the conductive regions of theconductive layer refer to the space between the regions extending in thex-dimension. The interstices of an electrically responsive element maycontain polymeric nonconductive material. The interstices may also bereferred to as nonconductive regions.

The term “reference plane” refers to an imaginary plane in relation to athree-dimensional object. For example, a reference plane oriented in ay-z plane is coincident and parallel to the surface of the conductiveregions of the conductive layer, or to a face of an article orelectrically responsive element. The reference plane is perpendicular tothe x-dimension and parallel to the cutting plane(s). The referenceplane may also be a cutting plane.

The words “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the invention.

As used herein, “a,” “an,” “the,” “at least one,” and “one or more” areused interchangeably. The term “and/or” (if used) means one or all ofthe identified elements/features or a combination of any two or more ofthe identified elements/features.

The term “and/or” means one or all of the listed elements/features or acombination of any two or more of the listed elements/features.

The above summary is not intended to describe each embodiment or everyimplementation of the present invention. Rather, a more completeunderstanding of the invention will become apparent and appreciated byreference to the following Description of Exemplary Embodiments andclaims in view of the accompanying figures of the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the subject wound dressing are described hereinwith reference to the drawings wherein:

FIG. 1 is a plan view of one embodiment of a wound dressing according tothe present invention.

FIG. 2 is a cross-sectional view of the wound dressing of FIG. 1 takenalong line 2-2 in FIG. 1.

FIG. 3 is a cross-sectional view of the wound dressing of FIGS. 1 and 2located over a wound W.

FIG. 4 is a plan view of the interior surface of an exemplary medicaldressing including a stand-off element and a valve.

FIG. 5 is a schematic representation of an electroactive actuator havingat least two electrically responsive elements.

FIG. 6 is a schematic representation of a unit cell.

FIG. 7 is a schematic representation of a first device having aconductive coating on both faces.

FIG. 8 is a schematic representation of a second device coated with aninsulative layer.

FIG. 9 is a schematic representation of an article comprisingelectrically responsive elements repeating in the x-dimension.

FIG. 10 is a schematic representation of an article having at least twoelectrically responsive elements presented in the x-, y- andz-dimensions.

FIG. 11 is a schematic representation of an article comprisingelectrically responsive elements repeating in the z-dimension.

FIG. 12 is a schematic representation of an unit cell viewed in the y-zplane along face 120.

FIG. 13 is a schematic representation of an unit cell viewed in the y-zplane along face 130.

FIG. 14 is a schematic representation of a top view of an article havingtwo electrically responsive elements as viewed in an x-y plane.

FIG. 15 is a schematic view of the wound dressing and micropump system,wherein the micropump is mounted on the wound dressing.

FIG. 16 is a view similar to the view of FIG. 3 illustrating the wounddressing and micropump system wherein the micropump is in fluidcommunication with the wound dressing.

FIG. 17 is a block diagram of components that may be supplied in oneexemplary embodiment of a wound dressing kit.

FIG. 18 is an exemplary embodiment of a tubular micropump.

FIG. 19 is an exemplary embodiment of a tubular micropump.

FIG. 20 is an exemplary embodiment of a diaphragm micropump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description of preferred embodiments of the invention,reference is made to the accompanying figures of the drawing which forma part hereof, and in which are shown, by way of illustration, specificembodiments in which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.

The composite wound dressing apparatus of the present disclosurepromotes healing of a wound via the use of a micropump system. Fluidremoved from the wound dressing may include gases and/or liquids (whichmay contain dispersed solid particles such as necrotic tissue, bloodclots, etc.). The fluid removal can be performed without removing orotherwise disturbing the medical dressing. Without limitation on thegenerality of the useful applications of the present invention, thedressing may be applied over surgical wounds, cosmetic surgicalprocedures, burns, cuts, scrapes and ulcers of various types, e.g.diabetic, decubitus, peripheral vascular disease, venous stasis andtrauma ulcers.

As used herein, the term “sealed environment” means that fluids (andsolids) from the ambient atmosphere surrounding the exterior of amedical dressing attached over a wound cannot freely enter the sealedenvironment. The sealed environment preferably includes a hermetic sealbetween the medical dressing and the surface surrounding the wound suchthat a negative pressure can be maintained in the sealed environment. Itmay, for example, be preferred that the medical dressing be capable ofholding (at least temporarily as described herein) a vacuum of 100 mmHg(i.e., a pressure that is 100 mmHg below atmospheric pressure) andperhaps a vacuum as much as 200 mmHg. Although some conventional medicaldressings can provide such a sealed environment, the medical dressingsof the present invention can do so while also offering the opportunityto remove fluids (liquids and/or gases) into and out of the sealedenvironment through at least one opening provided as a part of themedical dressing.

Fluid removal from the sealed environment may be useful to providenegative or reduced pressure therapies to a wound over which the medicaldressing is located. In a preferred embodiment, the sealed environmentcreated by a medical dressing of the present invention may preferably bemaintained at a negative pressure (i.e., pressure below the ambientatmospheric pressure) in the absence of active vacuum source in fluidcommunication with the sealed environment. In other words, the medicaldressings of the present invention may be used to maintain a sealedenvironment with a negative or reduced pressure in the periods betweenactive removal of fluids from the sealed environment. As a result, themedical dressings can provide a negative or reduced pressure environmentwith only intermittent or periodic fluid removal.

Although the magnitude of the negative pressure maintained in the sealedenvironment by the medical dressings will typically deteriorate overtime (after reaching a maximum during that active removal of fluids fromthe sealed environment), it may be preferred that the medical dressingbe capable of maintaining the negative pressure for at least somesignificant period of time. In some embodiments, it may be preferredthat the medical dressing be capable of maintaining at least some levelof negative pressure in the sealed environment (in the absence of activefluid removal) for a period of 1 minute or more, 5 minutes or more, 10minutes or more, 15 minutes or more, 30 minutes or more, or even 60minutes or more.

Deterioration of the negative pressure within the sealed environmentdefined by the medical dressing may be caused by a variety of sources.For example, some of the deterioration may be due to the diffusion ofgas into the sealed environment through the backing of the medicaldressing and/or the adhesive attaching the medical dressing to asubject. Another source of negative pressure deterioration in the sealedenvironment may be caused by gases and/or liquids entering the sealedenvironment from the subject (i.e., through the wound itself and/or thetissue surrounding the wound).

Although the medical dressings of the present invention may be used toprovide negative pressure wound therapy, in some instances fluids orother materials may potentially be delivered into the sealed environmentthrough the medical dressing by the micropump. It may be preferred thatthe delivery of materials into the sealed environment through themedical dressing by the micropump does not functionally compromise theability of the medical dressing to define a sealed environment asdescribed herein.

To retain a negative pressure within the sealed environments, it may bepreferred that the openings in the medical dressings be one-way valves.In other words, it may be preferred that the valve allows fluid flow inone direction (out of the sealed environment) and restricts or preventsflow in the opposite direction (into the sealed environment).Alternatively, the valve allows fluid flow in one direction (into thesealed environment) and restricts or prevents flow in the oppositedirection (out of the sealed environment).

In various embodiments, the medical dressings may include stand-offelements to provide open fluid pathways to the valves (that resistclosing under negative pressure in the sealed environment), barrierelements (to limit clogging of the valves); septum elements, and/orclosure elements. The closure elements may, in some instances, beprovided over the valves, such that the valves are sealed shut until theclosure elements are removed.

One exemplary embodiment of a wound dressing according to the presentinvention is depicted in FIGS. 1, 2, and 3. The wound dressing 12includes a backing 21 (which may preferably be conformable as describedherein). The backing 21 includes two opposed major surfaces: an interiorsurface 22 and an external surface 24. In use, the interior surface 22faces a wound (or other body site) over which the dressing is placedwhile the external surface 24 faces away from the wound (or other bodysite).

Potentially suitable materials for the wound backing 21 are described inmore detail below, but functionally, the backing 21 is preferably madeof materials that serve as a barrier to both liquid and rapid gasdiffusion. The barrier properties of the backing 21 may or may not beabsolute, e.g., the backing 21 may allow for limited passage of gas,although the backing 21 (and the other components of the dressing 12)preferably provide sufficient barrier properties to the passage of gassuch that, when placed over a wound, an adequate vacuum environment canbe at least temporarily applied to the treatment area. For example, thebackings may preferably have relatively high moisture vapor transmissionrates, but be substantially impervious to liquids.

The dressing also includes an adhesive on the interior surface of thebacking layer such that the dressing can be adhered to a subject over awound with the interior surface facing a wound. The adhesive 39 maycover all or part of the interior surface 22 in a continuous and/orpattern coated fashion. The adhesive 39 as depicted in FIG. 2 isprovided only around the perimeter or border of the backing 21 such thatthe adhesive 39 forms a frame around a central part of the interiorsurface 22 of the backing 21. Many other arrangements are possible. Onearrangement is depicted in FIG. 3 in which the dressing 12 is locatedover a wound W while the adhesive 39 is attached to the tissue (e.g.,skin) surrounding the wound W. The dressing 12, along with the wound Wand the tissue surrounding the wound, preferably define a sealedenvironment in which the wound W is isolated from the surroundingenvironment. The interior surface 22 of the backing 21 faces the sealedenvironment in which the wound is located while the external surface 24of the backing 21 faces away from the wound W.

The adhesive 39 as depicted in FIGS. 1 and 2 may preferably be exposedon only a portion of the interior surface 22 of the backing 21. In theembodiment depicted in FIGS. 1 & 2, the adhesive 39 is provided on onlya portion of the interior surface 22 (i.e., the central portion of theinterior surface 22 is free of the adhesive 39). In other embodiments,however, adhesive may be provided over substantially all of the interiorsurface 22 with a portion of the adhesive covered by another elementsuch that only a portion of the adhesive remains exposed for attachmentto a subject.

In any embodiment, however, it may be preferred that the adhesive 39extend continuously around the entire perimeter of the backing 21 suchthat the dressing 12, when attached to a subject, can form a sealedenvironment over a wound, with the bounds of the sealed environmentbeing defined by the interior surface 22 of the backing 21 as adhered tothe subject over a wound by the adhesive 39.

In preferred embodiments the dressings are adapted for easy deliver tothe wound. This may be done, for example, using handles and optionally astiffening strip as disclosed in U.S. Pat. Nos. 6,742,522 and 5,979,450incorporated herein by reference or by using a so called “framedelivery” as disclosed in U.S. Pat. Nos. 6,169,224, 5,088,483, and4,598,004 also incorporated herein by reference.

The adhesive is typically protected by a liner. Liners that are suitablefor use in the adhesive composites of the present invention can be madeof kraft papers, polyethylene, polypropylene, polyester or composites ofany of these materials. The liners are preferably coated with releaseagents such as fluorochemicals or silicones. For example, U.S. Pat. No.4,472,480, the disclosure of which is hereby incorporated by reference,describes low surface energy perfluorochemical liners. The preferredliners are papers, polyolefin films, or polyester films coated withsilicone release materials. Examples of commercially available siliconecoated release papers are POLYSLIK™ silicone release papers availablefrom James River Co., H. P. Smith Division (Bedford Park, Ill.) andsilicone release papers supplied by Daubert Chemical Co. (Dixon, Ill.).The most preferred liner is 1-60BKG-157 paper liner available fromDaubert, which is a super calendared Kraft paper with a water-basedsilicone release surface. Alternatively the wound dressing may belinerless and delivered in roll form such as described in U.S. Pat. No.5,803,086.

The wound dressing is preferably a single piece but may be formed fromtwo or more pieces that come together to form seams as taught in U.S.Pat. No. 4,969,880 incorporated herein by reference.

In some embodiments, it may be preferred that the medical dressinginclude absorbent material such as a wound packaging material, to absorbfluids (e.g., liquids) entering the sealed environment. Examples ofpotentially suitable absorbent materials may include, but are notlimited to, hydrophilic foams, woven materials, nonwoven materials, etc.and combinations thereof. It may be preferred that the absorbentmaterial be both absorbent and capable of releasing at least some(preferably a majority) of any absorbed fluids when a vacuum is appliedto the sealed environment through a valve. By releasing absorbed fluidsduring the removal of fluids from the sealed environment, the ability ofthe absorbent material to absorb fluids may be regenerated—which mayprolong the useful life of the medical dressing.

The wound dressing 12 further may include a normally-closed valve 30that is attached to the backing 21 over one or more passages that areformed through the backing 21. The valve allows fluid to be removed fromthe sealed environment defined by the wound dressing. Fluid flow throughthe one or more passages in the backing 21 is controlled by the valve30. The valve 30 (preferably be a one-way valve) may be connected to themicropump or be in fluid communication with the micropump. It may bepreferred that the micropump include a seat that can seal against theexternal surface of the backing of the wound dressing to provide afluid-tight seal. The valve may then be used to provide a vacuumenvironment to a wound over which the dressing 12 is placed as describedherein. Although the wound dressing depicted in FIGS. 1 and 2 includesonly one valve 30, wound dressings of the present invention may includemore than one valve if additional access to the sealed environmentdefined by the dressing is desired. Exemplary valves for this purposeare more completely described in Applicant's copending application U.S.Ser. No. 61/042,338, filed Apr. 4, 2008 and incorporated by reference inits entirety.

Another optional feature that may be included in some embodiments of themedical dressings of the present invention is a stand-off element thatmay be located proximate the valve on the interior surface of thebacking to assist in the removal of fluids from the sealed environment.FIG. 4 is a plan view of the interior surface 422 of the backing 420 ofa medical dressing 410. The medical dressing 410 may include adhesivethat is exposed over the entire interior surface 422 except for the areaoccupied by the stand-off element 450. The adhesive may be continuous orpattern-coated, although regardless of the coating, it may be preferredthat the adhesive be capable of providing a hermetic seal such that anegative pressure can be obtained in the sealed environment. One exampleof a potentially suitable pattern for pattern-coated adhesive may be agrid pattern. It may be preferred that the valve 430 be located withinthe area of the backing 420 that is occupied by the stand-off element450, although in some embodiments, the valve 430 may be locatedproximate the perimeter of the stand-off element 450.

The stand-off element 450 includes some form of structure on one or moresurfaces that provides open fluid pathways such that fluids within thesealed environment defined by the medical dressing 410 can be removedthrough the valve 430. If, for example, a stand-off element 450 is notprovided and the interior surface 422 of the dressing 410 were to sealagainst a wound or the skin surrounding a wound, the removal of fluidsfrom the sealed environment by the micropump could be hindered. Thestand-off element 450, however, preferably is capable of maintainingopen fluid pathways to facilitate fluid removal through the valve 430even when the sealed environment is at a negative pressure relative toatmosphere, that is, the fluid pathways preferably resistcollapsing—even under negative pressure.

Although the medical dressing depicted in FIG. 4 includes only onestand-off element 450 and one valve 430, the medical dressings of thepresent invention may include, for example, more than one valve inconnection with that same stand-off element. The use of multiple valvesmay be beneficial if, for example, one of the valves is poorly placedrelative to the sealed environment, malfunctions, becomes clogged, etc.In another variation, the medical dressings of the present invention mayinclude more than one stand-off element, with each of the stand-offelements potentially associated with one or more valves to facilitatefluid removal from the sealed environment. The use of more than onestand-off element in connection one medical dressing may be beneficialif, for example, one of the stand-off elements is poorly placed relativeto the sealed environment, becomes clogged, etc.

The stand-off elements used in the medical dressings of the presentinvention may take a wide variety of forms. In some embodiments, thestand-off element may be formed directly in the interior surface of thebacking (by, e.g., embossing, abrading, molding, cutting, etc.). Inother embodiments, the stand-off element take the form of a separatearticle (e.g., a film, etc.) having channels or other structuresembossed, abraded, molded, cut, or otherwise formed therein. Theseparate article forming the stand-off element may preferably beattached to the backing by any suitable technique or combination oftechniques (e.g., adhesives, heat sealing, thermal welding, etc.).

The channels in the stand-off elements may be in any pattern or shape,such as, but not limited to a honeycomb pattern of channels, grid orpartial grid, series of grooves (that are, e.g., parallel, radial,etc.), posts or other discrete structures (e.g., pyramids, etc.). Insome instances where the stand-off element is provided as an articlethat is separate from the backing of the medical dressing, the articlemay include fluid pathway-forming structures on both major sides of thestand-off element. Examples of some potentially suitable stand-offelements may be further described in, e.g., U.S. Patent ApplicationPublication No. US 2007/0172157 (Buchman), U.S. Pat. No. 6,420,622(Johnston et al.), etc.

Fluids delivered to the sealed environment through the medical dressingmay include gases (e.g., oxygen, nitric oxide, ozone, etc.) and/orliquids (e.g., saline, water, etc.). Particulates may, in someinstances, also be delivered to the sealed environment if, e.g., theyare entrained within a fluid delivered into the sealed environment.

In some instances, it may be desirable to deliver one or more activeagents to the sealed environment (and, thus, the wound covered by thedressing). The active agents may be provided as a fluid and/or may becarried within a fluid that is delivered to the internal volume. Somepotentially suitable active agents may include, e.g., antimicrobials,antibiotics, analgesics, healing factors such as vitamins, growthfactors, nutrients and the like. Examples of other potentially suitableagents may be described in U.S. Pat. No. 6,867,342.

If delivered, an active agent (or agents) could be supplied to thesealed environment continuously or intermittently. For example, anactive agent could be delivered to the sealed environment and allowed toremain in place (i.e., resident) for a selected period of time (e.g.,several hours) followed by, e.g., delivery of a second active agent,delivery of negative pressure therapy, etc. The initial active agentcould be removed before delivery of the second agent or it could beallowed to remain in place. Alternatively, the sealed environment couldbe rinsed with, e.g., saline or another flushing solution before placingthe sealed environment in a negative pressure condition, before deliveryof a second agent, etc.

As discussed herein, the medical dressings of the present invention maybe used for negative pressure wound therapy by providing a micropump inthe medical dressing through which fluid can be removed from a sealedenvironment defined by the medical dressing. The fluid is removed fromthe sealed environment using a micropump that can preferably be attachedto the medical dressing. It may be preferred that the micropump includea seat or valve that can seal against the external surface of thebacking of the medical dressing to provide a fluid-tight seal.

To remove fluid from the sealed environment, the pressure surroundingthe exterior of the valve can be sufficiently reduced to open the valveand remove fluid from the sealed environment through the valve. It maybe preferred that the valve be a normally-closed one-way valve such thatthe valve recloses when the reduced pressure environment is no longerpresent around the exterior of the valve (i.e., the pressuredifferential across the valve falls below the level needed to maintainthe valve in the open configuration). As discussed herein, the negativepressure can preferably be maintained within the sealed environmentdefined by the medical dressing.

In preferred embodiments, the wound dressing and micropump system of thepresent invention be capable of quickly connecting with each other toform a fluid-tight seal during removal of fluids from the sealedenvironments defined by the wound dressings. The wound dressing itselfmay preferably be featureless (e.g., present only the smooth externalsurface of the backing), while the pump includes a seat that provides asurface capable of sealing against the featureless backing to form therequired fluid-tight seal.

In some embodiments, the wound dressings and micropump may include moreconventional connections/fittings to provide a fluid-tight connectionbetween the micropump and the wound dressings. In such an embodiment,the wound dressing kit may include a fitting that attaches to theexternal surface of the backing using, e.g., a pressure sensitiveadhesive, etc. The fitting may, for example, include a tubing connector,Luer lock fitting, etc. designed for connection to the micropump. Theadhesive used to attach the fitting to the wound dressing may bereleasable, i.e., the fitting may potentially be removed from thedressing while the dressing remains in place over a wound, such that anysealed environment defined by the wound dressing remains intact duringremoval of the fitting.

The wound dressing micropump system includes a micropump that applies asubatmospheric pressure to the wound to effectively draw wound fluid orexudate out of the wound bed and encourage interstitial fluid to flowinto the wound bed from surrounding tissues. Hence, the wound dressingapparatus in the form of wound dressing and micropump system isextremely portable which allows the patient greater mobility than isavailable when an external vacuum source is used. The micropump of thepresent invention is sufficiently small to allow even greater mobilitythan other semi-portable configurations wherein the patient must carrythe micropump in a support bag, as is disclosed for example in US PatentApplication Publication No. 2007/0055209. The patient does not need tobe restricted for any period of time while the wound is being treated.

In contrast to known negative pressure therapy systems, the presentinvention utilizes a micropump which contacts the wound fluid directly.The excess wound fluid is passed through the micropump. Thus, themicropump is preferably self priming and able to pump out air trappedbetween the sealed dressing and the wound bed, although manual removalof air by manipulation of the wound dressing and/or micropump is alsocontemplated. In operation the micropump is turned on and the air ispumped out creating a vacuum. As used herein the term “vacuum” refers topressures less than the surrounding atmospheric pressure. Preferably thepressure is reduced by 5-250 mm mercury (Hg) (e.g. down to an absolutepressure of 500-740 mmHg but this will depend on the atmosphericpressure). When the pressure is reduced by more than 250 mmHg thepatient may experience pain. Thus, preferably the pressure is notreduced by more than 200 mmHg and more preferably by not more than 175mm Hg. Preferably, the pressure is reduced by at least 5 mmHg, 25 mmHg,more preferably at least 50 mmHg and most preferably at least 75 mm Hgin order to remove sufficient interstitial fluid.

Preferably the micropump is a low cost micropump designed to bedisposable. Disposing of the micropump with each dressing change reducesthe risk of bacterial contamination of the wound and transmission toother patients. Preferred micropumps are positive displacementmicropumps in order to ensure they are rapid, and preferably selfpriming. Many micropump designs are suitable including those driven bysmall electric motors such as micro-gear, lobe, piston, screw,peristaltic, centrifugal, and diaphragm pumps. Most preferred are thediaphragm pumps and electroresponsive micropumps as further describedbelow that do not require a motor. These micropumps inherently have fewmoving parts and thus are more reliable and able to operate veryquietly.

The micropumps of this invention preferably can achieve an outputpressure of at least 100 mmHg above atmospheric pressure (gaugepressure). Preferably the micropumps are capable of an output pressureof at least 200 mmHg above atmospheric pressure. The micropumps shouldbe capable of flow rates of at least about 1 ml/hr. More preferably themicropumps are capable of flow rates of at least about 3 ml/hr.

One such micropump may be made using electroactive material to form anactuator as further described below and in Applicant's copendingapplication U.S. Ser. No. 11/684,700, filed on Mar. 12, 2007 andincorporated by reference in its entirety. The micropump comprises apump chamber having an electroactive actuator on at least one face, ameans of bringing fluid (gas or liquid including liquid with dispersedsolids such as wound fluid) into and out of the pump chamber, a means ofrestricting the fluid movement outward when the chamber is filling and ameans of restricting the fluid movement inward when the chamber isemptying, and a means of supplying power to the electroactive actuatorat the proper voltage, frequency and amperage.

In one embodiment, the micropump comprises at least three elements: anelectroresponsive element, a pair of electrodes capable of applying avoltage potential across the thickness of at least a portion of theelectroresponseive element, and a power supply capable of applying theappropriate voltage drop to attain the required compression. Preferablythe power (voltage drop) may be adjustable to apply intermittent orvariable pressure for example by incorporation of a potentiometer. Theelectroresponsive element is preferably capable of achieving 0.01%strain, preferably 0.1% strain, more preferably 1% strain, even morepreferably 3% strain and most preferably greater than 5% strain when avoltage is applied. The most preferred electroresponsive elements areelectroactive polymers such as elastomers (polyurethanes, siliconerubber, Zetpole, VHB), visco-elastic polymers, and copolymers orterpolymers (PVDF, PVDF-TrFE, PVDF-HFP, PVDF-TrFE-HFP etc.) as furtherdescribed below. The electroresponsive element also may be polymercomposite film such as polymer-ceramics wherein the ceramic element maybe PZT, PZN-PT, Polymer-carbon nanotubes, carbon fibers, Polyamide-PZTfibers etc.

The electroactive material can be multilayer film as disclosed inApplicant's copending application U.S. Ser. No. 11/684,700, filed onMar. 12, 2007 and incorporated by reference in its entirety. Themultilayer film construction helps to significantly reduce the drivingvoltage and better control of driving force. In this multilayerconstruction, the voltage is applied to the individual layers, resultingtheir collective movement. Reducing actuator film thickness can reducethe driving voltage significantly. In this multilayer construction, thestiffness of the diaphragm can be easily controlled by the numbers oflayers while keeping the same driving voltage.

Alternatively, or in addition to the electroactive polymers describedherein, the electroresponsive element can be a magnetorestrictivematerial. A magnetorestrictive material as used herein is one thatchanges dimension by application of a magnetic field. A preferredmagnetorestrictive material is Terfenol-D. For example, suitablemagnetorestrictive materials may be Ferromagnetic Shape Memory AlloyMaterials (FSMA) that exhibit a twinning mechanism similar to thatobserved in traditional shape memory alloy materials such as NiTi andCuZn. In the FSMA the shape change may be initiated using an appliedmagnetic field. Another material investigated is an iron/gallium alloytermed Galfenol at the Naval Surface Warfare Center (Clark et al.). SeeClark, A. E., “Magnetostrictive rare earth-Fe₂ Compounds,” inFerromagnetic Materials: A Handbook on the Properties of MagneticallyOrdered Substances Vol. 1, Wolfarth, E. P., ed., 531-589, 1980. In theseapplications, a current, rather than voltage, may be used to drive thedisplacement of the actuator comprising magnetorestrictive materials.

A representative electroresponsive actuator 5 comprises first 100 andsecond 105 electrically responsive elements as illustrated in FIG. 5. Anelectrically responsive element 100 is further described in U.S. Pat.No. 4,627,138 (Im); U.S. Pat. No. 5,997,880 (Friedl et al.); U.S. Pat.No. 5,153,859 (Chatigny et al.); and International Publication No. WO02/096647A1 (Hilmas et al.). Electroresponsive actuator 5 comprisesfirst 100 and second 105 electrically responsive elements, which areunpoled, and extend along an x-dimension. Each of the electricallyresponsive elements 100, 105 has three mutually orthogonal dimensions,an x-, a y- and a z-dimension. The elements 100, 105 contain alternatingconductive 40, 41 and nonconductive 42 layers. The conductive layers 40,41 comprise regions 43, 53, 44, 54 of polymeric conductive material 49and regions 48 of polymeric nonconductive material 47; and thenonconductive layer 42 comprises polymeric nonconductive material 47.The electroresponsive actuator 5 further comprises a cutting plane 20which is useful for separating the first 100 and second 105 elements.The cutting plane 20 is perpendicular to the x-dimension and parallel tothe y-z plane.

The first 40 and second 41 conductive layers each have conductiveregions 43, 53, 44, 54. The first conductive layer 40 has first 43 andsecond 53 conductive regions, and the second conductive layer 41 hasthird 44 and fourth 54 conductive regions. The conductive regions 43,53, 44, 54 are arranged as illustrated in FIG. 5, so that a firstsurface 43 a, 53 a of first 43 and second 53 conductive regions of firstconductive layer 40 and a second surface 44 b, 54 b of third 44 andfourth 54 conductive regions of second conductive layer 41 arealternatingly exposed to one of two opposing faces 120, 130 of theelements 100, 105. The first 120 and second 130 faces are coincident tofirst 43 a, 53 a and second surfaces 44 b, 54 b of each respectiveconductive region 43, 53 and 44, 54. Further, first 120 and second 130opposing faces are parallel to the cutting 20, 24 and reference planes10. The two faces 120, 130 are exposed to recover a singleelectronically responsive element 100 after separation at one or morecutting planes 20 or at a reference plane 10 and a cutting plane 20.

The x-dimension refers to the width or cross-web dimension, they-dimension refers to the depth or down-web dimension, and thez-dimension refers to the thickness or height of the electroresponsiveactuator 5 having at least two electrically responsive elements 100,105. Analogously, the y-z plane corresponds to a plane having y- andz-dimensions, whereas an x-z plane corresponds to a plane having x- andz-dimensions. The x-y plane corresponds to a plane having x- andy-dimensions.

The x-dimension of the electroresponsive actuator 5 comprising at leasttwo elements 100, 105 refers to the width or cross-web dimension of theelectroresponsive actuator 5, and the subsequent electrically responsiveelements 100, 105 resulting from the electroresponsive actuator 5 afterseparating at a cutting plane 20. The x-dimension of an element 100 maybe in a range of 0.01 micrometer to 1 centimeter. Preferably, thex-dimension is in a range of 1 micrometer to 0.1 centimeter, and morepreferably, the x-dimension is in a range of 10 micrometers to 0.01centimeter.

The y-dimension relates to the length or down-web dimension of anarticle comprising at least two elements 100, 105. The y-dimension alsorefers to the elements 100, 105 after separation by a cutting plane 20from the electroresponsive actuator 5. The elements 100, 105 may eachhave a specific y-dimension as determined by a given application. Theelement 100 may be separated from the electroresponsive actuator 5 inthe x-z plane, which is perpendicular to the y-dimension. They-dimension of the element 100 may be in a range of 0.01 micrometer to 1centimeter. Preferably, the y-dimension is in a range of 1 micrometer to0.1 centimeter, and more preferably, the y-dimension is in a range of 10micrometers to 0.01 centimeter.

The z-dimension relates to the thickness or height of anelectroresponsive actuator 5 comprising at least two electronicallyresponsive elements 100, 105. The z-dimension may vary with respect tothe number of alternating layers of conductive and nonconductivematerial as the material is extruded through a die orifice of anextrusion apparatus and the degree of drawdown of the multiple layersduring coextrusion. The z-dimension of each of the elements 100, 105 maybe in a range of 3 micrometers to 3 millimeters. The z-dimension of theelectroresponsive actuator 5 after exiting the die orifice may bedifferent relative to the z-dimension of the electroresponsive actuator5 after draw down. Preferably, the z-dimension is in a range of 10micrometer to 0.5 millimeters, and more preferably, the z-dimension isin a range of 25 micrometer to 0.05 millimeters.

In FIG. 5, the first 100 and second 105 electrically responsive elementsof electroresponsive actuator 5 have first 20 and second 24 cuttingplanes, and a reference plane 10. The reference plane 10 of the articlemay also function as one of the cutting planes 20, 24. The reference 10and cutting planes 20, 24 each are parallel with respect to one other inthe y-z plane, and similarly to the faces 120, 130 of the elements 100,105. The reference 10 and cutting 20, 24 planes separate the elements100, 105 from one other exposing the alternating layers of conductivematerial 49 of the conductive layers 40, 41 on one of the two faces 120,130. Separation of the elements 100, 105 may be accomplished withtechniques including die cutting, laser cutting, shear slitting, scoreslitting, hot wire engaged slitting and combinations thereof. A trimportion or inoperative element of the electroresponsive actuator 5extending in the x-direction away from either of the faces 120, 130 mayresult after separation of the elements 100, 105 at a reference 10 orcutting 20, 24 planes. The trim portion or inoperable element maycomprise irregularly shaped surfaces or faces formed during extrusionthrough a die orifice and drawdown of the electroresponsive actuator 5.The trim portion may be recycled for other applications.

The electroresponsive actuator 5 contains alternating conductive 40, 41and nonconductive 42 layers extending in the z-dimension as illustratedin FIG. 5. The alternating conductive 40, 41 nonconductive 42 layers arecontinuous in the y-dimension. The conductive layers 40, 41 arediscontinuous in the x-dimension, and comprise polymeric conductivematerial 49. The nonconductive layer 42 comprises nonconductivepolymeric material 47 which is continuous in the x-dimension.

The first 40 and second 41 conductive layers of FIG. 5 each comprise atleast two conductive regions. The first conductive layer 41 containsfirst 43 and second 53 conductive regions, and the second conductivelayer 41 contains third 44 and fourth 54 conductive regions. Conductiveregions 43, 53 and 44, 54 are discontinuous in the x-dimension, andcontinuous in the y-dimension. First conductive region 43 of the firstconductive layer 40 has a first surface 43 a, second surface 43 b, athird surface 43 c, and a fourth surface 43 d. Second conductive region53 of the first conductive layer 40 has a first surface 53 a, secondsurface 53 b, a third surface 53 c, and a fourth surface 53 d.Conductive regions 43, 53 are discontinuous in the x-dimension havinginterstices 25 containing nonconductive material 47. Similarly, thirdconductive region 44 of the second conductive layer 41 has a firstsurface 44 a, second surface 44 b, a third surface 44 c and a fourthsurface 44 d. Fourth conductive region 54 of the second conductive layer41 has a first surface 54 a, a second surface 54 b, a third surface 54c, and a fourth surface 54 d. Third and fourth conductive regions 44, 54are also discontinuous in the x-dimension having interstices 25containing nonconductive material 47. Nonconductive layer 42 comprisesnonconductive material 47 which extends continuously in the x- andy-dimensions.

A cross-section of electroresponsive actuator 5 as illustrated in FIG. 5has at least two electrically responsive elements 100, 105 in the x-zplane. The cross-section shows a nonconductive layer 42 having a third42 c and fourth 42 d surfaces. The nonconductive layer 42 is located inbetween a first 40 and second 41 conductive layers. The first conductivelayer 40 is adjacent to the third surface 42 c of the nonconductivelayer 42, and the second conductive layer 41 is adjacent to the fourthsurface 42 d of the nonconductive layer 42. The first conductive layer40 has at least first 43 and second 53 conductive regions, and thesecond conductive layer 41 has at least third 44 and fourth 54conductive regions, where the interstices 25 between conductive regions43, 53, 44, 54 may contain a polymeric nonconductive material 47.Conductive regions 43, 53 and 44, 54 of conductive layers 40 and 41,respectively, repeat in the x-dimension.

FIG. 6 illustrates an electrically responsive element 100, 105 of anelectroresponsive actuator 5, where each element 100, 105 is made from aunit cell 15. The unit cell 15 comprises at least one nonconductivelayer 42 comprising nonconductive material 47, which has third 42 c andfourth 42 d surfaces that are continuous along two substantiallyorthogonal axes, the x- and y-dimensions. The unit cell 15 furthercomprises at least first 40 and second 41 conductive layers comprisingconductive material 49 that are discontinuous in the x-dimension, wherethe first conductive layer 40 comprises a first conductive region 43,and the second conductive layer 41 comprises a third conductive region44. First conductive region 43 has a first surface 43 a, a secondsurface 43 b, a third surface 43 c, and a fourth surface 43 d. Thirdconductive region 44 has a first surface 44 a, a second surface 44 b, athird surface 44 c, and a fourth surface 44 d. The first surface 43 a ofthe first conductive region 43 of the first conductive layer 40 iscoincident with a reference plane 10, where the second surface 43 b ofthe first conductive region 43 does not extend to the cutting plane 20.The second surface 44 b of the third conductive region 44 of the secondconductive layer 41 is coincident with a cutting plane 20, where thefirst surface 44 a of the third conductive region 44 does not extend tothe reference plane 10. The reference 10 and cutting 20 planes areparallel in a y-z plane. The unit cell 15 comprises alternating layershaving a nonconductive layer 42 in between the first conductive layer 40and the second conductive layer 41.

The unit cell 15 of FIG. 6 comprises first 120 and second 130 opposingfaces. The first face 120 is parallel to the reference plane 10, and thesecond face 130 is parallel to a cutting plane 20. The reference 10 andcutting 20 planes are parallel in the y-z plane. Electrically responsiveelements 100, 105 are separable at a cutting plane 20 and/or referenceplane 10 where the first surface 43 a of the first conductive region 43and the second surface 44 b of the third conductive region 44 areexposed on the first 120 and second 130 opposing faces, respectively.

The unit cell 15 of FIG. 6 illustrates a nonconductive layer 42 having athird surface 42 c adjacent to the fourth surface 43 d of the firstconductive region 43 of the first conductive layer 40. The fourthsurface 42 d of the nonconductive layer 42 is adjacent to the thirdsurface 44 c of the third conductive region 44 of the second conductivelayer 41. The interstices 25 may contain polymeric nonconductivematerial 47.

The electronically responsive elements 100, 105 of the electroresponsiveactuator 5 of FIG. 5 are unpolarized for use as components of a groupselected from actuators, sensors, pyroelectric devices, capacitors, andpiezoelectric devices. These elements 100, 105 typically comprisealternating layers of conductive and nonconductive materials. The numberof layers of an element 100 may be defined by the design of the layeringassembly used with appropriate extrusion equipment or other processconsiderations. Similarly, the dimensions of an element 100 may besubject to the design of a particular construction and a defined userapplication.

In one embodiment, the conductive 40, 41 and nonconductive 42 layers ofan element 100 of FIG. 5 have controlled thicknesses. The thickness ofthe layers is based on the layering assembly 400 design andcorresponding downstream extrusion equipment. The element 100 preferablyhas conductive layers 40, 41 that are as thin as possible for subsequentuse in a device without losing conductivity. The nonconductive 42 andconductive 40, 41 layers are typically symmetrical and preferably asthin as possible in order to maximize the electrical conductivity of theelements within a device. The first 120 and second 130 opposing facesare used to separate first 100 and second 105 elements at cutting planes20, 24 and/or reference plane 10. The cutting 20, 24 and/or reference 10planes expose the first surface 43 a of first conductive region 43, andthe second surface 44 b of the third conductive region 44 to the first120 and second 130 opposing faces of the elements 100, 105 asillustrated in FIG. 6.

In one embodiment, the unit cell 15 of FIG. 6 may be used as componentof a first device 600 illustrated in FIG. 7. The first device 600 may becoated with a second conductive material 510 on the first 120 and second130 opposing faces. The first surface 43 a of the first conductiveregion 43 and the second surface 44 b of the third conductive region areexposed at the first 120 and second 130 faces of FIG. 6, respectively.The first device 600 may comprises additional alternating conductive 40,41 and nonconductive 42 layers extending in the z-direction.

The second conductive material 510 used to electrically interconnect theexposed surfaces 43 a, 44 b of the conductive regions 43, 44 of FIG. 7on faces 120, 130 may be of many types. Examples include, but are notlimited to, solder, silver, other conductive metals, conductive polymersand polymers containing conductive fillers. The second conductivematerial 510 is preferably applied across each of the opposing faces120, 130 so as to electrically interconnect all of the exposed surfaces43 a, 44 b of the conductive regions 43, 44 to either of the faces 120,130. Conducting wires may be further attached to the second conductivematerial 510 followed by poling of the first device 600.

FIG. 8 illustrates a second device 610 having an insulative coating orlayer 520. The device 610 may be further coated with an insulative layer520 on faces 120, 130 and any remaining faces in the x-y and x-z planes.The insulative layer 520 of second device 610 assists in reducingmoisture and vapor penetration of the first and second conductive layers40, 41, as well as to reduce the possibility of electrical discontinuityacross the second device 610.

A device 610 comprising an element 100 having thin layer thicknessestypically has a voltage level of less than 10 volts. As the thickness ofthe layers decreases, the lower the applied driving voltage needed for agiven application. The device 610 may also have a modulus of elasticityin a range of 0.1 MPa-10 GPa.

FIG. 9 illustrates an article 180 having at least first 100 and second105 electrically responsive elements, where the elements 100, 105 arerepeating in the x-dimension. The elements 100, 105 are separable by oneor more cutting planes 20, 24. The exposed first 120 and second 130opposing faces of the elements 100, 105 result from separation of theelements 100, 105 at the cutting 20, 24 and/or reference 10 planes.First conductive layer 40 comprises first 43 and second 53 conductiveregions which are discontinuous in the x-dimension. Similarly, third 44and fourth 54 conductive regions of the second conductive layer 41 arediscontinuous in the x-dimension. The elements 100, 105 are made fromthe unit cell 15 as illustrated in FIG. 6.

In one embodiment, the electroresponsive actuator 5 of FIG. 5 contains aplurality of electronically responsive elements 100, 105, where theelements are separable by n−1 cutting planes 20, 24. The cutting planes20, 24 are perpendicular to the x-dimension of the article. A pluralityof elements 100, 105 comprises n unit cells 15 having n−1 cutting planes20, 24, wherein n is at least 3.

In one embodiment, article 180 comprises first 100 and second 105electrically responsive elements repeating in the x-dimension of FIG. 9.The elements preferably comprise symmetrical nonconductive 42 andconductive 40, 41 layers. Preferably, the electrically responsiveelements 100, 105 repeat in the x-dimension in a range of 2 to 1000 unitcells 15. More preferably, the elements 100, 105 repeat in a range of 5to 500 unit cells 15, and more preferably in a range of 25 to 250 unitcells 15. Further, the elements 100, 105 extend continuously in they-dimension as illustrated in FIG. 10. The unit cells 15 may extend inthe z-dimension resulting from the number of nonconductive 42 andconductive 40, 41 layers selected as well as the thickness of theindividual layers after symmetrically drawing down the nonconductive 42and conductive 40, 41 layers through an extrusion die.

FIG. 10 illustrates a three-dimensional perspective of electroresponsiveactuator 5 having at least two electrically responsive elements 100, 105separable at cutting 20, 24 and reference 10 planes. Conductive layers40, 41 are continuous in the y-dimension, and discontinuous in thex-dimension. Nonconductive layer 42 alternates with the conductivelayers 40, 41 where the nonconductive layer 42 is continuous in the x-and y-dimensions. Nonconductive material 47 occupies the interstices 25between conductive regions 43, 53 of first conductive layer 40, andconductive regions 44, 54 of the second conductive layer 41.

FIG. 11 illustrates article 190 having at least first 100 and second 105electrically responsive elements, where the elements 100, 105 havealternating conductive 40, 41 and nonconductive 42 layers repeating inthe z-dimension. The elements 100, 105 are separable at cutting planes20, 24. As similarly illustrated in FIG. 5, the first 40 conductivelayer comprises first 43 and second 53 conductive regions, and thesecond 41 conductive layer comprises third 44 and fourth 54 conductiveregions repeating in the x-dimension. The cutting planes 20, 24 forseparating the elements 100, 105 are perpendicular in the x-dimension.The separation of the elements 100, 105 along cutting planes 20, 24 ofarticle 190 may result in multilayered elements for specificapplications.

FIG. 12 illustrates a cross-sectional view in the y-z plane of element100. The first face 120 of element 100 shows alternating conductive 40and nonconductive 42 layers. In the y-z plane, the layers include afirst conductive layer 40, and a nonconductive layer 42. In thez-dimension, the element 100 comprises first conductive layer 40,nonconductive layer 42, nonconductive material 47 of nonconductiveregion 48 of second conductive layer 41 as illustrated in FIG. 5,followed by a nonconductive layer 42. Nonconductive material 47 may fillthe interstices 25 or nonconductive region 48 located between theconductive regions of the first conductive layer 40, where a conductiveregion does not extend to the reference plane 10 of first face 120.Conductive layer 40 comprises polymeric conductive material 49 of firstconductive region 43, which is continuous in the y-dimension. Multiplealternating conductive 40 and nonconductive 42 layers may be coextrudedfor forming a multilayered element 190 extending in the z-dimension ofFIG. 11.

FIG. 13 illustrates a cross-sectional view in the y-z plane of element100. The second face 130 of element 100 shows alternating conductive 41and nonconductive 42 layers. In the y-z plane, the layers includenonconductive material 47 of nonconductive region 48 of first conductivelayer 40 as illustrated in FIG. 5, a nonconductive layer 42, and asecond conductive layer 41, followed by a nonconductive layer 42.Nonconductive material 47 fills the interstices 25 or nonconductiveregion 48 of first conductive layer 40 of FIG. 12 between the conductiveregions. Second conductive layer 41 comprises polymeric conductivematerial 49 of third conductive region 44, which is continuous in they-dimension.

FIG. 14 illustrates a cross-sectional view in an x-y plane ofelectroresponsive actuator 5 comprising at least first 100 and second105 electrically responsive elements separable at cutting planes 20, 24and/or reference plane 10. Elements 100, 105 are shown with first 43 andsecond 53 conductive regions of the first conductive layer 40 havinginterstices 25 filled with a nonconductive material 47. The firstsurface 43 a of the first conductive region 43 is coincident withreference plane 10, where the second surface 43 b does not extend to thefirst cutting plane 20. Similarly, the first surface 53 a of secondconductive region 53 of the first conductive layer 40 is coincident withthe first cutting plane 20, where the second surface 53 b does notextend to the second cutting plane 24. Third surface 43 c of a firstconductive region 43 and third surface 53 c of second conductive region53 are the uppermost surfaces in the x-y plane illustrated in FIG. 14.

Each of the alternating conductive layers 40, 41 may be made ofdifferent materials or combinations of materials which may furthercomprise particles or fillers for conductivity. Similarly, each of thenonconductive layers 42 may include the analogous material orcombination of materials to that used in the conductive layers 40, 41,although each individual nonconductive layer 42 may include differentmaterials or combinations of materials from the other nonconductivelayers. The nonconductive layers 42 may further comprise particles toenhance electrical conductivity of an element 100 of a device.

In one embodiment, the first polymeric material and organic particlesform a polymeric conductive material 49 of the conductive layers 40, 41.

In one embodiment, a first polymeric material is elastomeric.

Thermoplastic materials that have elastomeric properties are typicallycalled thermoplastic elastomeric materials. Thermoplastic elastomericmaterials are generally defined as materials that exhibit highresilience and low creep as though they were covalently crosslinked atambient temperatures, yet process like thermoplastic nonelastomers andflow when heated above their softening point. Thermoplastic elastomericmaterials useful in the conductive layer and/or the nonconductive layeras a first polymeric material or one of a blend of polymeric materialsinclude, for example, linear, radial, star, and tapered block copolymerssuch as those described below.

Examples of a first polymeric material include silicone elastomers,acrylic elastomers, polyurethanes, polybutadienes, thermoplasticelastomers, polybutadiene-acrylonitrile copolymers and combinationsthereof.

In one embodiment a first polymeric material is a thermoplastic.

Examples of a thermoplastic first polymeric material include pressuresensitive adhesives, fluoropolymers and polymers comprising silicone andacrylic moieties, and the like. Examples of fluoropolymers includehomopolymers such as polyvinylidene difluoride (PVDF), copolymers suchas polyvinylidene fluoride-trifluoroethylene P(VDF-TrFE), polyvinylidenefluoride-chlorofluoroethylene P(VDF-CFE), polyvinylidenefluoride-hexafluoropropylene P(VDF-HFP), polyvinylidenefluoride-trifluoroethylene-chlorofluoroethylene P(VDF-TrFE-CFE),polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethyleneP(VDF-TrFE-CTFE), polyvinylidenefluoride-tetrafluoroethylene-chlorotrifluoroethylene, polyvinylidenefluoride-trifluoroethylene-hexafluoropropylene, polyvinylidenefluoride-tetrafluoroethylene-hexafluoropropylene, polyvinylidenefluoride-trifluoroethylene-tetrafluoroethylene, polyvinylidenefluoride-tetrafluoroethylene, polyvinylidenefluoride-trifluoroethylene-vinyl fluoride, polyvinylidenefluoride-tetrafluoroethylene-vinyl fluoride, polyvinylidenefluoride-trifluoroethylene-perfluoro(methyl vinyl ether), polyvinylidenefluoride-tetrafluoroethylene-perfluoro(methyl vinyl ether),polyvinylidene fluoride-trifluoroethylene-bromotrifluoroethylene,polyvinylidene fluoride-tetrafluoroethylene-bromotrifluoroethylene,polyvinylidene fluoride-tetrafluoroethylene-chlorofluoroethylene,polyvinylidene fluoride-trifluoroethylene-vinylidene chloride, andpolyvinylidene fluoride-tetrafluoroethylene-vinylidene chloride andcombinations thereof.

Examples of organic conductive particles or fillers include graphite,carbon nanotubes, carbon black, and combinations thereof. Thesematerials may be added to the first polymeric material to form apolymeric conductive material 49 for the conductive layers 40, 41. Thefirst polymeric material may be mixed, blended, compounded or by othermeans with organic materials or fillers to achieve a uniform mixture ofmaterials suitable for forming conductive layers 40, 41.

In one embodiment, the first polymeric material may be blended or mixedwith inorganic particles to form conductive layers 40, 41. Examples ofinorganic particles or fillers include silver, copper, nickel, aluminum,platinum, palladium, derivatives and combinations thereof. Thesematerials may have irregular shapes or defined structures suitable forforming conductive layers 40, 41.

In one embodiment, the first polymeric material may be blended or mixedwith inorganic coated particles to form conductive layers 40, 41.Examples of inorganic materials used for coating particles include gold,silver, palladium, platinum and combinations thereof.

In one embodiment, the first polymeric material may form the polymericconductive material 49 of the conductive layers 40, 41. Examples of afirst polymeric material, which is conductive includepoly(3,4-ethylenedioxy thiophene), polyaniline, polypyrrole,polythiophene, polydiacetylene, polyacetylene, polyisothianaphthene,polyheteroarylene-vinylene, wherein the heteroarylene group can forexample be thiophene, furan or pyrrole, poly-p-phenylene, polyphenylenesulphide, polyperinaphthalene, polyphthaloxyanine, copolymers of andphysical mixtures thereof. The first polymeric material may beconductive with optional particles or fillers.

Optional additives to combine with the conductive first polymericmaterial may further include dopants, doping agents and combinationsthereof. Doping agents comprises iodine, peroxides, Lewis acids andprotic acids for doping by oxidation, sodium, potassium and calcium fordoping by reduction.

The nonconductive layer 42 comprises a polymeric nonconductive material47. The polymeric nonconductive material 47 may comprise a firstpolymeric material as described above. Mixtures or blends of the firstpolymeric material with other polymeric materials may be utilized toform a nonconductive layer 42. Additives to increase the dielectricconstant may be added or compounded with the first polymeric material ofnonconductive layer 42. Examples additives include BaTiO₃, leadzirconate titanate (PZT), PT (lead titanate) composites, PTCa andcombinations thereof. These additives may be compounded with the firstpolymeric material.

The conductive polymeric material 49 and the nonconductive polymericmaterial 47 have sufficient viscosity to be extruded or coated onto anadjacent layer of the electroresponsive actuator 5. An extrudableformulation of a blend of conductive polymeric materials 49, as well asa blend of a conductive polymeric material 49 with a nonconductivematerial 47 may be utilized.

The first polymeric material of the conductive layers 40, 41 may includeconductive polymers, polymeric materials or a blend of polymericmaterials rendered conductive. In some instances, the first polymericmaterial is mixed with organic materials to yield a conductive layer.

The nonconductive 42 and conductive 40, 41 layers being continuous inthe y-dimension or the down-web dimension are substantially uniform inthickness to plus or minus 10 percent. Similarly, it is desirable tohave thin conductive layers, where the thickness of these layers may begoverned by the average diameter or size of the particles to be blendedwith the first polymeric materials.

The multilayer construction can be obtained by multilayer extrusionprocess as described in U.S. Pat. No. 4,627,138. In another multilayerextrusion process, the conductive layer (also referred to as anelectrode) can be patterned as further described in Applicant'scopending application U.S. Ser. No. 11/684,700, filed on Mar. 12, 2007and incorporated by reference in its entirety. This process helps tocontrol of the desired size of actuator rather than having full widthdepending upon the die lip as described in above patent. Methods forcoextruding multiple layer webs, and related equipment are described inU.S. Pat. Nos. 6,949,283 (Kollaja et al.) U.S. Pat. No. 5,825,543(Ouderkirk et al.) and U.S. Pat. No. 5,783,120 (Ouderkirk et al.).

Multilayer construction can also be achieved by laminating eachelectroactive layer having electrode layers on the top and bottom. Thelamination process can be done in multiple ways such as using adhesive,heat lamination, using solvent (such as described in U.S. Pat. No.5,997,800) to soften the top surface.

Micropumps

The micropumps used in connection with the medical dressings of thepresent invention may take any suitable form. In some embodiments, themicropumps may be portable, self-contained devices, while in otherembodiments the micropumps may be fixed, stationary systems. In someinstances, fluids may even be removed from a sealed environment definedby the medical dressings using suction developed by a person using theirmouth (in, e.g., a battlefield or other remote location).

Examples of some potentially suitable micropumps that may be used withand/or supplied in a kit with the medical dressings of the presentinvention may include the pumps described in U.S. Patent ApplicationPublication No. US 2007/0209326 (Tretina), although many other pumps maybe used in place of the pumps disclosed therein. Although the pumpsdescribed in the document identified above include a power source (e.g.,a battery), micropumps used in connection with the present invention maybe manually powered. Examples of some other potentially suitablemanually powered pumps may include, e.g., devices that include resilientcavities that can be compressed and, when returning to theirpre-compression states, provide a vacuum force at the inlet of the pump(e.g., bulbs, hemovacs, etc.).

In some embodiments, the wound dressing and micropump system of thepresent invention may preferably include one or more traps or fluidcollection components capable of collecting and retaining liquids (and,in some embodiments, gases) removed from the sealed environments definedby the medical dressings. The traps may be integral with the micropumpsin some embodiments, while in other embodiments the traps may beseparate from the micropumps such that the traps may be replaced withoutrequiring replacement of both the micropumps and the traps. Examples ofsome potentially suitable traps that are designed to separate liquidsfrom the removed fluids may be described in, e.g., U.S. PatentApplication Publication Nos. US 2007/0209326 (Tretina) and US2007/0172157 (Buchman).

It may be preferred that the medical dressings of the present inventionand any micropumps used therewith to remove fluids from sealedenvironments be capable of quickly connecting with each other to form afluid-tight seal during removal of fluids from the sealed environmentsdefined by the medical dressings. The medical dressing itself maypreferably be featureless (e.g., present only the smooth externalsurface of the backing), while the micropump includes a seat thatprovides a surface capable of sealing against the featureless backing toform the required fluid-tight seal.

In some embodiments, the medical dressings and micropumps may includemore conventional connections/fittings to provide a fluid-tightconnection between the micropumps and the medical dressings. Suchfittings may be useful where, e.g., the micropump is to be connected tothe medical dressing for an extended period of time, e.g., for more than2 minutes. In such an embodiment, the wound dressing may include afitting that attaches to the external surface of the backing using,e.g., a pressure sensitive adhesive, etc. The fitting may, for example,include a tubing connector, Luer lock fitting, etc. designed forlonger-term connection to a micropump. The adhesive used to attach thefitting to the medical dressing may be releasable, i.e., the fitting maypotentially be removed from the dressing while the dressing remains inplace over a wound, such that any sealed environment defined by themedical dressing remains intact during removal of the fitting.

Preferred pumps are micropumps. Preferred micropumps are diaphragm pumpshaving at least one deformable element. These micropumps may be actuatedby a number of means including the use of electroactive polymers (EAP),piezoelectric pumps using ceramic piezoelectric elements such as PZT,ionic Polymer Metal Composites (IMPC) as well as compositesincorporating carbon nanotubes or other conductive elements that enhancethe electroactive response.

Other preferred pumps include the Digital Pulse Activated Cell systempumps disclosed in US 2004/0234401, WO2006/065884, and US 2005/045210,the EAP Micropumps disclosed in herein which preferably comprisemultilayer EAP elements made, for example, as taught in U.S. Pat. No.4,627,138 as well as EAP pumps disclosed in Pope et. al. DielectricElastomer Laminates for Active Membrane Pump Applications, Proc. Of SPIEVol. 5385, 2004, pp 60-67; traveling wave pumps such as that describedin U.S. Pat. No. 5,961,298. Suitable EAP materials include polyurethanessuch as those disclosed in U.S. Pat. No. 5,977,685, polyacrylates suchas 3M Company VHB adhesive #4905, polyvinylidene fluoride (PVDF),polyvinylidene/trifluoroethyelne (VDF-TrFE), and silicones such as NusilCF19-2186.

The micropump comprises an inlet, an exit, and optionally a means forregulating the pressure. The micropump may be attached directly to thedressing or may be remote from the dressing but in fluid communicationwith the dressing by suitable means such as a tube. The micropumppreferably comprises a one way inlet valve and a one way exit valve toensure fluid is evacuated and not allowed to flow back into the woundbed. The valves may be of any design such conventional ball valves.Preferably, the valves are comprised of elastomeric elements (asdescribed herein). For example, preferred valves are umbrella orduckbill valves such as those available from Vernay Laboratories ofYellow Springs, Ohio.

A check valve or other means may be required to regulate pressure,particularly for pumps able to create a vacuum of more than 100 mmHgbelow atmospheric pressure. This may be accomplished via a check valvethat opens at a predetermined pressure drop and allows air into thewound bed. If a check valve is used it preferably has a membrane elementthat will filter out microorganisms and prevent them from entering thewound bed. Alternatively and preferably the micropump is equipped with apressure sensor and a control circuit that slows the pump speed at apredetermine pressure set point. The set point is preferably variableand easily set by the clinician. A read out of the pressure may bedesired. Alternatively, the micropump is self limiting and unable tocreate a vacuum more than the desired maximum vacuum, e.g. more thanabout 150 mmHg.

The micropump may be driven by AC or DC power and may be from a line orbattery source. Preferably the micropump is driven by a small disposablebattery source. The power source may be located in a package with themicropump or it may be at a remote site and connected to the micropump.Preferably, the battery is capable of driving the micropump for at least2 hours of continuous operation. More preferably, the battery is capableof driving the micropump for at least 8 hours, even more preferably atleast 1 day, more preferably still for multiple days of continuousoperation. Thus, the micropumps are more energy efficient to avoid theneed for large battery sources.

The micropump is preferably programmable to pull a continuous,intermittent or variable vacuum. For example, the micropump could beprogrammed to pull and hold a vacuum of 100 mmHG or be programmed topull a vacuum of 150 mmHg for a period of time following by a period oftime at a vacuum of 25 mmHg below atmospheric pressure in an oscillatoryfashion.

In a preferred embodiment, the micropump is secured directly to thewound dressing either through the interior portion of the dressing or atthe periphery. In either case an inlet tube may be unnecessary. Themicropump also can be remote from the dressing and attached via an inlettube. In such case, the micropump may have multiple inlets and exitports and/or multiple micropumps may be employed on a single dressing.Such inlet means may be a simple tube which passes fluid from the woundbed into the micropump. The inlet of the inlet tube may then need to beprotected by a porous filter element. The inlet means may be a simpleflexible tube or may be other means such as the fluid control articlesdescribed in U.S. Pat. No. 6,420,622 or the drain tubes described inU.S. Pat. No. 4,398,910.

When the micropump is not connected directly to the dressing it ispreferably a tubular configuration such as micropump embodiments shownin FIGS. 18 and 20 that can be sealed between the dressing and the skinsurface and pass between the wound bed (inlet) and the exterior.

The micropump exit is preferably in fluid communication with a reservoirfurther described below and designed to collect the excess wound fluid.The fluid reservoir may be a vented rigid container, a flexiblecontainer, or a vented flexible container. In a rigid container a ventis required in order to reduce or eliminate pressure build-up in thecontainer. The container may be a simple vacuum canister such as usedroutinely in surgery, a canister or it may be a simple deflated flexiblepouch that fills to capacity with excess wound fluid. The reservoir maybe empty or may be filled with an absorbent that solidifies the fluid asit absorbed. Preferably the reservoir is a flexible pouch similar tothat used in ostomy appliances and it may be flushable. It is asignificant advantage of this invention in which the reservoir is filledunder positive pressure that a rigid trap is not necessary, as opposedto vacuum systems which generally require rigid traps. Thus, the presentinvention can accommodate ambulatory patients by supplying a discretesystem of a wound dressing, micropump and interchangeable small fluidreservoir collection pouches. The collection pouch can be constructed ofany suitable polymeric material but is preferably an odor barrier suchas disclosed in U.S. Pat. No. 7,270,860. Furthermore, the collectionreservoir may have a means for alerting the patient or care giver thatit should be changed. This alert can be an electronic means or a passivemeans.

Preferred fluid reservoirs can be a flexible pouch similar to that usedin ostomy appliances such as those disclosed in U.S. Pat. No. 7,214,217.The pouches may even be flushable as disclosed in U.S. Pat. No.7,179,245. However, the fluid reservoir may be as simple as a vacuumcanister such as used routinely in surgery, a canister such as describedin U.S. Pat. No. 4,569,674.

A sample port may be provided between the micropump and the fluidreservoir or on the reservoir itself for easily obtaining a sample foranalysis. For example, a “T” shaped tubing may be provided in the exitline or a simple valved port on the fluid reservoir with a lure lock forattaching a syringe may be used. The sample can be used for analysis ofchemical or physical properties of the wound fluid in order to assesshealing or for further treatment means.

Wound Dressing Kits

The wound dressings of the present invention may potentially be suppliedin the form of a kit with one or more optional components. FIG. 17 is aschematic diagram of one kit 800. The kit 800 may preferably be providedin a sealed package (e.g., bag, pouch, tray, etc.). The kit 800 includesone or more wound dressings 810 of the present invention.

One or more micropumps 850 may also be provided in the kit 800, with themicropumps 850 attached to the wound dressing(s) 810 and/or provided asseparate articles for the user to attach at their discretion and or oneor more fittings 884 adapted for attachment to the external surfaces ofthe dressings 810 as discussed herein, where the fittings 884 can beused to provide connections between the wound dressing and/or valves inthe dressings 810 and the micropumps 850. The kit 800 may also includeone or more intermediate wound packing materials 870 as describedherein.

The kit 800 may also include one or more fluid collection bags orcannisters 882 that may be used with the one or more micropumps 850 tocollect fluids (e.g., liquids) that may be removed from sealedenvironments defined by the dressings 810 over wounds.

The following discussions will provide some non-limiting examples as tothe various features that may be provided in the embodiments of thepresent invention.

Electroactive Polymer Films

The electroactive actuator displacement can be further increased bymodifying the actuator structure. For example, mechanical structuresthat will enhance the displacement include multilayer laminates ofelectroactive materials, unimorph (e.g. a piezoelectric disk cemented toa thin metal disk), bimorph (e.g. a cantilever that consists of twoactive layers. For example, electrical activation of a piezoelectricbimorph cause one layer to extend and the other layer to contract),recurved benders, corrugated benders, spiral or helical designs. See,for example, Recurve Piezoelectric-Strain-Amplifying ActuatorArchitecture in IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 3, NO. 4,December 1998, 293, James D. Ervin and Diann Brei.Nonconductive polymermaterials are described in U.S. Pat. Nos. 6,605,246, 6,343,129, and5,977,585.

Nonconductive polymer actuator materials include fluoropolymers andpolymers comprising silicone and acrylic moieties, and the like.Examples of fluoropolymers include homopolymers such as polyvinylidenedifluoride (PVDF) copolymers such as polyvinylidenefluoride-trifluoroethylene P(VDF-TrFE), polyvinylidenefluoride-chlorofluoroethylene P(VDF-CFE), polyvinylidenefluoride-hexafluoropropylene P(VDF-HFP), polyvinylidenefluoride-trifluoroethylene-chlorofluoroethylene P(VDF-TrFE-CFE),polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethyleneP(VDF-TrFE-CTFE), polyvinylidenefluoride-tetrafluoroethylene-chlorotrifluoroethylene, polyvinylidenefluoride-trifluoroethylene-hexafluoropropylene, polyvinylidenefluoride-tetrafluoroethylene-hexafluoropropylene, polyvinylidenefluoride-trifluoroethylene-tetrafluoroethylene, polyvinylidenefluoride-tetrafluoroethylene, polyvinylidenefluoride-trifluoroethylene-vinyl fluoride, polyvinylidenefluoride-tetrafluoroethylene-vinyl fluoride, polyvinylidenefluoride-trifluoroethylene-perfluoro(methyl vinyl ether), polyvinylidenefluoride-tetrafluoroethylene-perfluoro(methyl vinyl ether),polyvinylidene fluoride-trifluoroethylene-bromotrifluoroethylene,polyvinylidene fluoride-tetrafluoroethylene-bromotrifluoroethylene,polyvinylidene fluoride-tetrafluoroethylene-chlorofluoroethylene,polyvinylidene fluoride-trifluoroethylene-vinylidene chloride, andpolyvinylidene fluoride-tetrafluoroethylene-vinylidene chloride. Otherpolymers include, polyurethane, silicone, fluorosilicone, naturalrubber, polybutadine, nitrile rubber, isoprene and combinations thereof.

Other suitable electroactive materials include: (a) Ceramic actuatormaterial containing lead such as lead zirconate titanate (PZT), leadzirconate niobate:lead titanate (PZN:PT), lead magnesium niobate:leadtitanate (PMN:PT), barium titanate (BaTiO₃); (b) Conductive polymerssuch as polyaniline, trans polyacetylene, polypyrrole, polythiophenes,polyethyldioxithiophene, carbon nanotubes etc.; (c) Ionic Polymer metalcomposite (IPMC) films, such as Nafion™ and Flemion™ orstyrene/divinylbenzene, perfluorinated alkenes based polymers doped withmetal ions such as Pt(NH₃)₄HCl; (d) Polymer gels actuators includepolyacrylonitrile, polyacrylic acid gel, polyacrylic acid-polyvinylalcohal; and any combinations of the foregoing.

Backings

The wound dressings of the present invention are useful in connectionwith any conformable backing that provides a sufficiently impermeablebarrier to the passage of liquids and at least some gases.Representative backings may include non-woven and woven fibrous webs,knits, films, foams polymeric films and other familiar backingmaterials. The preferred backing materials include thin elastomericbackings These types of backings help ensure conformability and highadhesion around the wound site. Preferred backing materials may betranslucent or transparent polymeric films including polyurethanes (e.g.ESTANE), polyether polyesters (e.g. HHTREL), polyether amides (e.g.PEGAX) as well as polyolefins (e.g. ENGAGE).

The backings used in connection with the present invention may be highmoisture vapor permeable film backings Issued U.S. Pat. Nos. 3,645,835and 4,595,001 describe methods of making such films and methods fortesting their permeability. The film (and any adhesive used thereon asdescribed herein) may transmit moisture vapor at a rate equal to orgreater than human skin. The adhesive-coated film may, e.g., transmitmoisture vapor at a rate of at least 300 g/m²/24 hrs/37° C./100-10% RH,more preferably at least 700 g/m²/24 hrs/37° C./100-10% RH, and mostpreferably at least 2000 g/m²/24 hrs/37° C./100-10% RH using theinverted cup method as described in U.S. Pat. No. 4,595,001.

The backings may also preferably be conformable to anatomical surfaces.As such, when the backing is applied to an anatomical surface, itconforms to the surface even when the surface is moved. The backing mayalso be conformable to animal anatomical joints. When the joint isflexed and then returned to its unflexed position, the backing maystretch to accommodate the flexion of the joint, but is resilient enoughto continue to conform to the joint when the joint is returned to itsunflexed condition. A description of this characteristic of backings canbe found in issued U.S. Pat. Nos. 5,088,483 and 5,160,315. Examples ofsome potentially suitable backings may include elastomeric polyurethane,polyester, or polyether block amide films. These films combine thedesirable properties of resiliency, high moisture vapor permeability,and transparency.

Commercially available examples of potentially suitable backingmaterials may include the thin polymeric film backings sold under thetradenames TEGADERM (3M Company), BIOSITE (Johnson & Johnson Company),OPSITE (Smith & Nephew), etc. Many other backings may also be used,including those commonly used in the manufacture of surgical incisedrapes (e.g., incise drapes manufactured by 3M Company under thetradename STERIDRAPE and IOBAN), etc.

Because fluids may be actively removed from the sealed environmentsdefined by the wound dressings of the present invention, a relativelyhigh moisture vapor permeable backing may not be required. As a result,some other potentially useful backing materials may include, e.g.,metallocene polyolefins and SBS and SIS block copolymer (e.g., KRATONtype) materials could be used.

Regardless, however, it may be preferred that the backings be keptrelatively thin to, e.g., improve conformability. For example, it may bepreferred that the backings be formed of (e.g., consist essentially of)polymeric films with a thickness of 200 micrometers or less, or 100micrometers or less, potentially 50 micrometers or less, or even 25micrometers or less.

Wound Packaging Material

In some embodiments, the wound dressings may be provided with woundpacking material in as an intermediate layer. The wound packing materialmay, in some embodiments, also function as a filter element as describedherein (although this function is not required). In some embodiments,the wound packing material may be resiliently compressible, such thatthe wound packing material can also optionally function as a ballastcomponent to assist in maintaining a negative pressure in the sealedenvironment as described herein. For example, when a vacuum is appliedthe resilient packing will be compressed. When the vacuum is removed andthe valve closed to seal the wound cavity the resilient packing willstill provide an expansion force in order to return to itsnon-compressed state. This expansion will serve to create or helpmaintain a vacuum for a period of time. Wound packing materials may beuseful where, e.g., the wound to be contained within the sealedenvironment is a chronic wound that is in the form of a significantdepression (which may, in some instances be tunneled under thesurrounding skin). When treating such wounds, it may be desirable toprovide wound packing material in the wound before applying a wounddressing to create a sealed environment over the wound.

The wound packing material may preferably be flexible such that it canfill and/or conform to the shape of the wound. The wound packing may beabsorbent or non-absorbent. The wound packing may preferably be capableof providing passageways through which fluids can pass. Some potentiallysuitable examples of wound packing materials may include fully orpartially reticulated foam (e.g., open cell polyurethane foams, etc.),fabric (e.g., gauze, mesh, woven, knit, or nonwoven materials),particulate materials, beads, etc. that may be placed in a wound to fillthe internal volume. If provided in particulate or bead form, theparticulates or beads may, in some embodiments, be contained within aflexible bag or other structure to facilitate removal of the woundpacking (unless, e.g., the wound packing material is bioabsorbableand/or biodegradable). A preferred polyurethane foam may be hydrophilicand capable of spontaneously absorbing deionized water such as WILSORBfoam (available from Illbruck). Preferred hydrophilic packing componentswill absorb a 100 microliter drop of deionized water when gently placedin contact with the foam in less than 60 seconds and preferably in lessthan 30 seconds.

Polyvinylalcohol (PVA) open cell foams may also be used. A preferredfabric is nonwoven fabric and more preferably a lofted nonwoven fabrichaving resiliency such that when compressed to 50% of its thicknessrebounds to 90% or greater of the original thickness in less than 10seconds and preferably in less than 1 second. A preferred loftedresilient nonwoven has physical properties similar to 3M Buff Puff™Facial Sponge. These structures may be treated to be hydrophilic andspontaneously wet with water. In some preferred embodiments theintermediate material may include several hydrophilic colloid materialsto absorb fluids. In other embodiments the intermediate layers arepreferably hydrophobic in order to retard tissue ingrowth. One skilledin the art will appreciate that there may be a number of materialssuitable for the intermediate layer to achieve various objectivesincluding combinations of the materials mentioned above and combinationsthat include other materials.

The intermediate layer can be secured directly to the dressing. Forexample, the intermediate layer can be secured via the pressuresensitive adhesive coating. In this embodiment the intermediate layer isplaced at least over the portion of the dressing where the micropumpinlet conduit will be located. This may be in the interior of thedressing or may be located at the periphery.

If the intermediate layer is provided in a form such that it is notattached to the wound dressing, the wound dressing may be provided inthe form of a kit including the wound dressing and the separate barrierelement and/or wound packing In using such a kit, the barrier elementand/or wound packing may be attached to the wound dressing before thewound dressing is delivered to a patient. Alternatively, theintermediate layer may be placed on or in the wound, with the wounddressing deployed over the wound after wound packing material is inposition. The wound dressing 210 can be used according to methods foruse with the other wound dressings, and includes the additional step ofplacing the intermediate material layer over at least a portion of thewound site.

Pressure Sensitive Adhesives

Suitable adhesive for use in wound dressing articles of the presentinvention include any adhesive that provides acceptable adhesion to skinand is acceptable for use on skin (e.g., the adhesive should preferablybe non-irritating and non-sensitizing). Preferred adhesives are pressuresensitive and in certain embodiments preferably have a relatively highmoisture vapor transmission rate to allow for moisture evaporation.Suitable pressure sensitive adhesives include those based on acrylates,polyurethanes, KRATON and other block copolymers, silicones, rubberbased adhesives (including natural rubber, polyisoprene,polyisobutylene, butyl rubber etc.) as well as combinations of theseadhesives. The adhesive component may contain tackifiers, plasticizers,rheology modifiers as well as active components including for example anantimicrobial agent.

The pressure sensitive adhesives that may preferably be used in thewound dressings of the present invention may include adhesives that aretypically applied to the skin such as the acrylate copolymers describedin U.S. Pat. No. RE 24,906, particularly a 97:3 iso-octylacrylate:acrylamide copolymer. Another example may include a 70:15:15isooctyl acrylate:ethyleneoxide acrylate:acrylic acid terpolymer, asdescribed in U.S. Pat. No. 4,737,410 (Example 31). Other potentiallyuseful adhesives are described in U.S. Pat. Nos. 3,389,827; 4,112,213;4,310,509; and 4,323,557. Inclusion of medicaments or antimicrobialagents in the adhesive is also contemplated, as described in U.S. Pat.Nos. 4,310,509 and 4,323,557.

The pressure sensitive adhesives may, in some embodiments, transmitmoisture vapor at a rate greater to or equal to that of human skin.While such a characteristic can be achieved through the selection of anappropriate adhesive, it is also contemplated in the present inventionthat other methods of achieving a high relative rate of moisture vaportransmission may be used, such as pattern coating the adhesive on thebacking, as described in U.S. Pat. No. 4,595,001. Other potentiallysuitable pressure sensitive adhesives may include blown-micro-fiber(BMF) adhesives such as, for example, those described in U.S. Pat. No.6,994,904. The pressure sensitive adhesive used in the wound dressingmay also include one or more areas in which the adhesive itself includesstructures such as, e.g., the microreplicated structures described inU.S. Pat. No. 6,893,655.

Release Liners

Release liners may be supplied with the wound dressings of the presentinvention to protect the pressure sensitive adhesive used to attach thedressings to the patient and create the sealed environment. Releaseliners that may be suitable for use in the wound dressing of the presentinvention can be made of supercalendered kraft paper, glassine paper,polyethylene, polypropylene, polyester or composites of any of thesematerials. The liners are preferably coated with release agents such asfluorochemicals or silicones. For example, U.S. Pat. No. 4,472,480describes low surface energy perfluorochemical liners. The liners maypreferably be in the form of papers, polyolefin films, polyolefin coatedpaper or polyester films coated with silicone release materials.Examples of commercially available silicone coated release liners arePOLY SLIK™ silicone release on polyolefin coated papers, FL2000™silicone release on film, and STICK-NOT™ silicone release onsupercalendered kraft paper, all available from Loparex Inc.,(Willowbrook, Ill.); silicone coated supercalendered kraft paper fromAkrosil, (Menasha, Wis.); and silicone release film from HuhtamakiFlorchheim, (Florchheim, Germany). Another potential liner is siliconecoated (1630) low density polyethylene available from Huhtamaki.

The selection of a specific release liner may be made in conjunctionwith the selection of a pressure sensitive adhesive. Those skilled inthe art will be familiar with the processes of testing a new adhesiveagainst different liners or a new liner against different adhesives toarrive at the combination of qualities desired in a final product. Theconsiderations pertinent to the selection of a silicone release linercan be found in Chapter 18 of the Handbook of Pressure SensitiveAdhesive Technology, Van Nostrand-Reinhold, 1982, pp. 384-403. U.S. Pat.No. 4,472,480 also describes considerations pertinent to the selectionof a perfluoropolyether release liner.

Carriers/Delivery Systems

In some instances, the backings used in the wound dressings of thepresent invention may be so flexible and supple such that when a releaseliner is removed from the backing, the backing may tend to fold andadhere to itself, interfering with the smooth, aseptic application ofthe dressing to a patient's skin.

Various delivery systems have been proposed to address this problem suchas those disclosed in U.S. Pat. No. 4,485,809; U.S. Pat. No. 4,600,001;and EPO Publication No. 0 051 935. Carrier-type delivery systems such asthose described in U.S. Pat. No. 6,685,682 offer an alternative deliverysystem for use with conformable backings

Alternative carriers and/or delivery systems may include frames,handles, stiffening strips, etc. as disclosed in issued U.S. Pat. Nos.6,742,522; 5,979,450; 6,169,224; 5,088,483; 4,598,004; D 493,230; etc.Still another potentially suitable delivery system may be described inU.S. Patent Application Publication No. US 2007/0156075 A1. In someinstances, the backings can be delivered linerless as described in,e.g., U.S. Pat. No. 5,803,086.

EXAMPLES

Exemplary embodiments of this invention are discussed and reference hasbeen made to possible variations within the scope of this invention.These and other variations and modifications in the invention will beapparent to those skilled in the art without departing from the scope ofthe invention, and it should be understood that this invention is notlimited to the exemplary embodiments set forth herein. Accordingly, theinvention is to be limited only by the claims provided below andequivalents thereof.

The invention will be further clarified by the following examples whichare exemplary and not intended to limit the scope of the invention.

Example 1

FIG. 15 is a cross-sectional schematic diagram of this example. ATegaderm™ (3M Company, Maplewood Minn.) wound dressing 102 is used toseal a wound cavity defined by the wound bed “WB” and the wounddressing. The wound cavity is filled with a wound packing 110. Adiaphragm micropump is fixed to the exterior surface of the wounddressing backing The micropump extracts fluid (air and wound exudate)and moves this fluid through the exudate collection line to a to aflexible collection pouch 150. Although shown with a single micropumpmultiple micropumps may be used over a single wound site. The collectionpouch is designed very similar to an ostomy bag and can be worn in asimilar manner. The collection pouch may be sealed or vented. In apreferred embodiment it is not vented. If vented, it may include a ventfilter to reduce order that may be generated from the wound fluid. Avalve is placed in the exudate collection line 140 which may be used tocollect samples of wound fluid for analysis.

Referring to FIGS. 15 and 16, the wound evacuation system 100 iscomprised of wound dressing 102, a base layer 108, a wound packing 110,a micropump 120, an evacuation line 140, and a wound fluid collectionpouch 150. The wound dressing, 102, is comprised of an elastomericpolyurethane film and adhesive as described in U.S. Pat. Nos. 5,088,483and 5,738,642. As supplied the dressing further comprises a disposablerelease liner (not shown) that protects the pressure sensitive adhesive(PSA), 106. The PSA, 106, is coated continuously over the entire surfaceof the wound dressing backing, 104. An orifice, 126, is made through thedressing that communicates with pump inlet opening 125. The pump inlet125 of the micropump leads to a chamber, 123, having a self sealingelastomeric one-way inlet valve, 122. Fluid enters the inlet chamberpasses into a pumping chamber 129 and exits through the exit chamber127. An exit valve, 124, is placed at the entrance to the outletchamber. The one-way inlet and exit valves are shown as an elastomericumbrella valve which may be obtained from Vernay Laboratories, YellowSprings, Ohio. Both umbrella valves are normally closed valves. Althoughshown with a single inlet and outlet valve, multiple inlet and multipleoutlet valves may be used. Importantly, we have found that the inlet andoutlet valves need to have a “cracking pressure”. That is, a finiteminimum pressure which causes them to open. This ensures a good seal.Without a good tight hermetic seal the micropump will not operate at lowflow rates. Thus, the umbrella valve elastomeric stem is designed to bestretched to provide a strain force sufficient to bias the valves into anormally close condition. Alternatively, duck bill valves may be usedthat have a defined cracking pressure. Duckbill valves also areavailable from Vernay Laboratories. The micropump also includes adiaphragm, 130, that is capable of displacement sufficient to move thefluid. The diaphragm is made of a thermoplastic polymer, thermosetpolymer, ceramic, metal, or combination thereof such as a laminate. Thediaphragm is necessarily resilient and will fully and rapidly recoverfrom any induced strain. Strain (displacement) is induced by the use ofan actuator. The actuator can be a solenoid, piezoelectric ceramic suchas PZT, a voice coil or an “internal actuator”. The internal actuatormeans that at least a portion of the diaphragm itself can function as anactuator. In one embodiment the internal actuator is a polyurethanematerial as disclosed in U.S. Pat. No. 5,977,685. In an alternativepreferred embodiment the internal actuator is a multilayerelectroresponsive polymer membrane (EPM) as described herein.Alternatively, the valves (122 and 124) and diaphragm, 128, may beeliminated and replaced with a digital pulse activated actuated pumpsystem as described in US Patent Application Publication No.2004/0234401 in which multiple actuators are in direct contact with thefluid. A preferred piezoelectric micropump is a 1/10 scale version of aModel BPH-414D piezoelectric pump available from MEDO USA.

This micropump is capable of pulling a vacuum of 161 mmHg belowatmospheric pressure without the need for priming. It is a desiredproperty of the micropumps that they be self-priming (i.e. no primingnecessary).

Alternatively the wound micropump can be made using a conductive polymerdiaphragm internal actuator as described in WO2005/042974 A1 andJP04015832. In this design the conductive polymer is driven to expandand contract by a chemical electrolytic mechanism requiring low voltage(e.g. less than 5 volts DC and typically 1-2 Vdc). Like the EAP anddigital pulse activated pump systems this type of actuator is silentallowing the micropump to make very little, if any, noise.

Multiple cells with smaller diaphragms may also be used to generatehigher inlet vacuum and higher exit pressure.

In operation, a battery sends current to the actuator which causes thediaphragm to displace up, down, or both up and down. This movementdisplaces the fluid in the pumping chamber creating a positive pressureat the exit valve and a negative pressure at the inlet valve. In oneembodiment the maximum vacuum (i.e. pressure less than atmospheric) isself limiting as determined by the actuator and valving parameters andis preset so the clinician does not have to worry about it.Alternatively, a controller may be provided that can allow the clinicianto adjust the flow rate and/or vacuum created. The battery may be adisposable battery such as a common watch, AAA, AA, alkaline battery, alithium ion battery, a lithium polymer battery, nickel cadmium battery,nickel metal hydride battery, and the like. It may be disposable orrechargeable. One or more batteries may be used and arranged in seriesor in parallel. A transformer or converter may be used in order to drivea direct current (DC) or alternating current (AC) actuator. The batteryis preferably secured to the patient at a location where they will notlie on it creating a potential pressure point. Once the micropump isactivated it is self priming and a vacuum will be applied to the woundcavity. The dressing shown in FIGS. 15 and 16 will likely be sucked intothe wound. This will be supported by the wound packing material 110.Preferred wound packing materials include hydrophobic open cellpolyurethane foam, open cell hydrophilic polyurethane foam such asAquazone foam available from Foamex International, Linwood, Pa. Foamsmay have pore sizes of 30-200 pores per inch but are preferably 50-150PPI. Densities may be from 1 to 5 lb/ft³ (16-80 kg/M³) but arepreferably 1.5 to 3 lb/ft³ (25-50 kg/M³). When sufficient fluid hasfilled the wound packing it will begin to enter the micropump andsubsequently be delivered through the evacuation line 140 to the woundfluid collection pouch 150. Alternatively, the wound packing material isa resilient nonwoven such as 3M Buff Puff™ (3M Company, Maplewood,Minn.). When the pouch becomes full a new pouch with integral evacuationline may be attached to the micropump. Alternatively, the pouch may beadapted to allow removal and attachment of the evacuation line.Preferably the pouch can be easily emptied into a toilet or other securedisposal. The collection pouch also may incorporate a superabsorbentpolymer that gels the wound fluid as it enters the pouch. In thismanner, the pouch can be disposed of in regular trash without concern ofleakage. The pouch also may contain more or more antimicrobial agents tokill any bacteria and prevent odor. Similarly, the wound packingmaterial may contain an antimicrobial agent or other medicament suitablefor treating wounds.

The wound dressing system also may comprise a wound contact layer 108.The wound contact layer may be a separate component but preferably isbonded to the wound packing material. Bonding may be accomplished bythermal or adhesive methods. FIG. 5 shows the wound contact layer as aseparate component. Suitable wound contact layers include Tegapore™, (3MCompany, Maplewood, Minn.) or XEROFLO™ (Kendall Corp. a division ofCovidien, Mansfield, Mass.). Other suitable wound contact layers includegels such as alginate gels and alginate fabrics such as Tegaderm™Alginate (3M Company, Maplewood, Minn.) or carboxymethylcellulosenonwoven fabrics such as Aquacel Ag (Convatec a division of E. R. Squibb& Sons, LLC, UK)

Example 2

The wound dressing evacuation system of Example 1 is employed exceptthat the micropump is supplied separately in a kit with the wounddressing. The kit comprises the micropump, wound dressing, wound packingmaterial with an integral (bonded) wound contact layer, evacuation lineand wound fluid exudate collection pouch. As in Example 1, the woundpacking/contact layer is cut to size and placed in the wound. Thedressing is placed over the entire wound making certain to seal well tothe surrounding tissue and forming a hermetic seal. The micropumpcomprises a pressure sensitive adhesive on its base. The micropump ispositioned over the preformed orifice in the dressing (126). In thisembodiment the micropump may be reusable (but preferably only on asingle patient) and applied to several dressings in succession asneeded.

Example 3

The wound dressing evacuation system of Example 2 is employed exceptthat the dressing is not supplied with an orifice. Instead the orificeis created by the clinician using a supplied punch which may be similarin operation to a hand held paper hole punch. The orifice may be placedanywhere on the dressing the clinician prefers such as in the center oralong the periphery. Multiple orifices and multiple micropumps areemployed.

Example 4

The wound dressing evacuation system of Example 1 is employed. Thehousing of the micropump must be rigid enough to prevent it fromcollapsing during operation. Thus, this can create a pressure point. Inorder to prevent further tissue damage in a patient who may lie on thewound the micropump is sealed in a conformable elastomer which acts as acushioning device and prevents sharp pressure points.

Example 5

The wound dressing evacuation system of Example 2 is employed exceptthat the wound dressing is supplied with a vacuum valve over theorifice. A film laminate vacuum valve is used such as that described inApplicant's copending patent application U.S. Ser. No. 61/042,338, filedApr. 4, 2008 and incorporated by reference in its entirety. A preferredvalve is which is commercially used on Reynolds Handi-Vac vacuum freezerbags (Alcoa Inc., Richmond, Va.).

Example 6

The wound dressing evacuation system of Example 1 is employed exceptthat the wound dressing is further augmented with an absorbent layer incombination with a hydrophobic foam packing The absorbent layer is ahydrogel such as that used in the dressings of U.S. Pat. No. 7,005,143.

Example 7

The wound dressing evacuation system of Example 2 is employed exceptthat the micropump is placed off the dressing and adhered to the skin orto a separate secural device. The micropump is connected to the wounddressing through an inlet line (tubing) and a port which is secured tothe dressing over the orifice with, for example, an adhesive, heat seal,or solvent weld.

Example 8

The wound dressing evacuation system of Example 1 is employed exceptthat the wound dressing further comprises a frame on the perimeter ofthe top surface in order to facilitate delivery as described in U.S.Pat. Nos. 5,088,483 and 5,738,642 which are incorporated herein byreference.

Example 9

The wound dressing evacuation system of Example 1 is employed exceptthat the wound dressing further comprises a microreplicated fluidcontrol feature on the inner (wound facing) surface in order tofacilitate transport of excess fluid to the micropump. Dressingsincorporating microreplicated fluid control features are described inU.S. Pat. No. 6,420,622 which is incorporated herein by reference.

Example 10

The wound dressing evacuation system of Example 7 is employed exceptthat a tubular micropump is employed. The tubular micropump comprises asection of elastomeric tubing separated by a one way inlet valve (e.g. aduckbill valve) and a one way exit valve. Along the tubing section isone or more means of depressing or squeezing the tubing to partially orcompletely collapse the walls together at one or more points along thetubing section. This may be accomplished using any of the actuatorsdescribed in Example 1. This is distinct from a peristaltic pump whichusing a rotating series of rollers to sequentially depress and movefluid along the tubing without valves. Examples of tubular micropumpsare shown in FIGS. 18-20.

Example 11 Elastomeric Electroactive Polymer Pump

The commercially available VHB-4910 and 4905 tapes from 3M Company(Maplewood Minn.) were used as an actuator film (pump diaphragm). Theactuator film was stretched 400% in the plane of the film (XYdirection).

The film was kept pre-stretched by stretching in over and securing it toa glass ring. Due to sticky nature of VHB tape, no other tape was use tostick the VHB to glass ring and also to make multilayer actuator films.The gold electrode was coated on the both sides of pre-stretched filmusing Pelco SC-6 sputter coater. A paper circular mask was used to getdesired shape (2.5 cm and 4 cm diameter) of the gold electrode. Thestrip of 2.0 mm×20 mm of 3M 1181 copper conductive tape was used to makeconnections at the edge of each gold coating.

In the case of multilayer actuator films, the first actuator film iscoated as explained above. The second actuator film was stretched 400%in both directions and than carefully laminated to first layer. The topelectrode of first layer is used as a bottom electrode of 2^(nd) layer.A strip of copper tape was attached to the gold electrode beforelaminating another layer.

After producing the desired multilayer actuator, polyurethane (Tegaderm1621) was laminated on the top of the actuator stack. The polyurethanefilm did not have any electrode on the top. This film was then removedfrom glass ring and laminated to the top cover of a pump housing. Thetop cover was placed on the bottom of the pump housing with thepolyurethane layer down.

The multilayer actuator diaphragm was activated (induced to move in theZ axis) by applying a AC voltage using Trek model #610E voltageamplifier connected with function generator HP 3314A. The 10 mmHgpressure was achieved using 5-layers of VHB and One layer ofpolyurethane film.

The arrangement produced is shown below.

Examples 12 and 13 Alternative Pump Designs Example 12 ConductivePolymer Pump

A conductive polymer micropump useful in this invention is commerciallyavailable from EAMEX Corporation, Osaka Japan and has an actuatorcomprising a modified polypyrrol polymer—(PPy-CF₃SO₃). The micropumpspecifications of a few of these micropumps are described below.

Size 25 × 22 × 3 mm 27 × 4 mm 30 × 6 mm Diameter of φ4 mm φ10 mm φ24 mmdiaphragm Number of cells 19 4 1 Pressure 70 kPa 55 kPa 40 kPa Flow 0.9ml/min 3 ml/min 6 ml/min Frequency 1 Hz 1 Hz 1 Hz Voltage 2 V 2 V 2 VCurrent 200 mA 200 mA 200 mA

Example 13 Piezoelectric Ceramic Pump

A piezoelectric micropump was purchased from BIMOR Pump, model #BPH-414Dserial #30805146 was purchased from MEDO USA Inc, Hanover Park, Ill.,60103 (http://www.nitto-europe.com/german/pumps/bimor/index.html). Theinlet pressure of 161 mmHg was measured. This micropump wasapproximately 7.5×6.8×2.5 cm in diameter. Thus, a ⅓ to 1/10 scale modelsmaller micropump would be particularly useful in the present invention.

Another piezoelectric micropump model #DTI-200-12.5P was purchased DEAKTechnologies Inc., Brooklyn, N.Y. The piezoelectric material is used forboth piezoelectric micropumps is PZT. This micropump has the followingdimensions:

Pump: 4.25 cm dia., Mounting flange, 6.25 cm dia., Height: 2.5 cm. Asmaller ½ to ⅕ scale model of this micropump is preferred for thepresent invention.

The complete disclosure of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated (although conflictsbetween any such disclosures and the descriptions explicitly providedherein should be resolved in favor of this document).

1.-74. (canceled)
 75. A wound dressing apparatus, which comprises: awound dressing member dimensioned for positioning relative to a woundbed; and a micropump system including a micropump for applyingsubatmospheric pressure to at least the wound dressing member tofacilitate removal of fluid from the wound bed, the micropump beingplaced in the wound or mounted to the wound dressing member; whereinfluid enters an inlet side of the micropump from the wound dressingmember and exits a fluid accumulation device under positive pressure.76. The wound dressing apparatus according to claim 75 wherein the wounddressing member includes a backing, an adhesive coated on the backing,and a wound packing layer.
 77. The wound dressing apparatus according toclaim 76 wherein the adhesive coated backing is secured about theperiphery of the wound to provide a seal between the wound dressingmember and tissue surrounding the wound bed.
 78. The wound dressingapparatus according to claim 75 wherein the wound dressing apparatusfurther includes an exudate collection line and an exudate collectiondevice.
 79. The wound dressing apparatus according to claim 78 whereinthe exudate collection device is a flexible disposable pouch.
 80. Thewound dressing apparatus according to claim 75 wherein the vacuumapplied by the micropump is self limiting and incapable of creating avacuum in excess of 200 mmHg below atmospheric pressure.
 81. The wounddressing apparatus according to claim 75 wherein the micropump comprisesan electroactive actuator member.
 82. The wound dressing of claim 75,wherein the backing comprises an interior surface and an externalsurface; an adhesive on at least a portion of the interior surface,wherein the adhesive extends around a perimeter of the interior surfaceof the backing to adhere the medical dressing to a subject over a wound;wherein, when the medical dressing is attached over the wound, themedical dressing defines a sealed environment over the wound, andfurther wherein operation of the micropump causes fluid within thesealed environment to be moved through at least one opening in thebacking
 83. The wound dressing of claim 75, wherein the micropump isrotorless and located proximate the backing
 84. The medical dressing ofclaim 75, wherein the dressing further comprises a normally-closed valveattached to the backing over an opening formed through the backing,wherein fluid flow through the opening is controlled by the valve, andwherein a dead volume between the normally-closed valve and the backingis 10 mm³ or less.
 85. A medical dressing according to claim 84, whereinthe valve comprises a one-way valve that permits fluid flow out of thesealed environment when in an open configuration and restricts fluidflow into the sealed environment when in a closed configuration.
 86. Amedical dressing according to claim 84, wherein the valve comprises aplurality of polymeric film layers aligned with the backing, wherein theplurality of polymeric film layers comprises a flap layer comprising aflap formed therein.
 87. A medical dressing according to claim 75,wherein the medical dressing further comprises a stand-off element,wherein the stand-off element defines plurality of fluid pathways to theopening on the interior surface of the backing when the stand-offelement is positioned proximate the interior surface of the backing inthe sealed environment.